refactor: use Bytes instead of Vec<u8> in CarBlock

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

• to improve the performance of iterating all CIDs in a Forest CAR with CarStream (e.g. Building indices of Forest CAR require iterating all CIDs without accessing data)

# main
Iterating lite_40320_5986246.forest.car.zst
loaded 120095076 blocks from lite_40320_5986246.forest.car.zst, took 4m 22s 936ms 105us 98ns

# PR
Iterating lite_40320_5986246.forest.car.zst
loaded 120095076 blocks from lite_40320_5986246.forest.car.zst, took 3m 49s 148ms 266us 6ns

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Refactor

  • Internal improvements to data structure handling for enhanced efficiency.
  • Updated caching mechanism for better resource management.
  • Adjusted dependency configuration to support additional features.

• Tests

  • Updated test implementations for consistency.

[coderabbitai]

Walkthrough

This PR migrates the CarBlock payload field from Vec<u8> to bytes::Bytes across the codebase. The change includes updating the core CarBlock struct definition, adding the bytes crate feature to build dependencies, updating cache layer types, and converting all construction sites to use explicit .into() conversions for byte payload handling.

Changes

CarBlock Bytes Type Migration

Layer / File(s)	Summary
Core CarBlock Type Definition src/utils/db/car_stream.rs	CarBlock struct field changes from Vec<u8> to Bytes; CarBlock::from_bytes parsing uses cursor.into_inner() directly as Bytes instead of to_vec().
Workspace Dependency & Parsing Cargo.toml	Adds bytes feature to get-size2 workspace dependency to support bytes crate integration.
Cache Layer Type Updates src/db/car/mod.rs	ZstdFrameCache LRU cache value type changes from Vec<u8> to Bytes; public signatures updated: get() returns Option<Option<Bytes>>, put() accepts HashMap<CidWrapper, Bytes>; test helper gen_index generates Bytes values.
Blockstore Implementation Updates src/db/car/forest.rs	ForestCar::get cache-hit and collision-decode paths return Vec<u8> via to_vec() instead of cached value directly.
CarBlock Construction Site Updates src/blocks/tipset.rs, src/chain/mod.rs, src/db/memory.rs, src/tool/subcommands/archive_cmd.rs, src/rpc/methods/state.rs	All sites constructing CarBlock use explicit .into() conversion for the data field: data: payload.into().
Task::Emit Payload Type Update src/ipld/util.rs	Task::Emit variant payload type changes from Option<Vec<u8>> to Option<Bytes>; ChainStream and IpldStream emit handling wraps blockstore data with .into() for conversion; tipset header block enqueue sites pass .into() to Emit tasks.
Test Assertion & Validation Updates src/db/car/forest.rs, src/db/parity_db/gc.rs, src/tool/subcommands/car_cmd.rs, src/utils/db/car_stream/tests.rs, src/utils/db/car_util.rs	Test assertions convert blockstore results to Bytes before comparison; car_cmd validate function compares using Bytes::from(block.data); test helpers construct CarBlock with .into() conversions.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• ChainSafe/forest#6901: Both PRs perform the same Vec to bytes::Bytes migration pattern across caching and blockstore components.
• ChainSafe/forest#5841: Both PRs modify get-size dependency and LRU cache value types to bytes::Bytes.
• ChainSafe/forest#5868: Both PRs modify Task::Emit and src/ipld/util.rs block data handling related to CAR block construction.

Suggested reviewers

• LesnyRumcajs
• akaladarshi

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main refactoring: replacing Vec with Bytes in CarBlock across the codebase.
Docstring Coverage	✅ Passed	Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hm/opt-car-block

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/opt-car-block

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/tool/subcommands/car_cmd.rs`:
- Line 120: The current validation masks DB/index errors by using
.ok().flatten(), so replace that silent conversion with proper error propagation
and context: call db.get(&block.cid) and propagate errors using ? plus
.context(...) (or .with_context(...)) to attach a helpful message, then flatten
the Option and map(Bytes::from) into a variable (e.g., stored) and use
anyhow::ensure!(stored == Some(block.data), "validation mismatch: ...") to
report mismatches; reference the db.get(&block.cid) call and the ensure!
comparison so you update the exact expression that currently reads
db.get(&block.cid).ok().flatten().map(Bytes::from) == Some(block.data).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 08e2edf0-f5a4-4ad4-a965-2163fcd3a015

📥 Commits

Reviewing files that changed from the base of the PR and between 9259f45 and 95bd88b.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (14)

• Cargo.toml
• src/blocks/tipset.rs
• src/chain/mod.rs
• src/db/car/forest.rs
• src/db/car/mod.rs
• src/db/memory.rs
• src/db/parity_db/gc.rs
• src/ipld/util.rs
• src/rpc/methods/state.rs
• src/tool/subcommands/archive_cmd.rs
• src/tool/subcommands/car_cmd.rs
• src/utils/db/car_stream.rs
• src/utils/db/car_stream/tests.rs
• src/utils/db/car_util.rs

[codecov]

Codecov Report

❌ Patch coverage is 67.79661% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.24%. Comparing base (8f2b32b) to head (95bd88b).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/rpc/methods/state.rs	0.00%	12 Missing ⚠️
src/ipld/util.rs	69.23%	4 Missing ⚠️
src/db/parity_db/gc.rs	66.66%	0 Missing and 2 partials ⚠️
src/tool/subcommands/archive_cmd.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/blocks/tipset.rs	84.88% <100.00%> (+0.08%)	⬆️
src/chain/mod.rs	76.85% <100.00%> (ø)
src/db/car/forest.rs	83.87% <100.00%> (+0.09%)	⬆️
src/db/car/mod.rs	85.71% <100.00%> (ø)
src/db/memory.rs	88.81% <100.00%> (ø)
src/tool/subcommands/car_cmd.rs	77.93% <100.00%> (+0.46%)	⬆️
src/utils/db/car_stream.rs	71.42% <100.00%> (-0.36%)	⬇️
src/utils/db/car_util.rs	88.88% <100.00%> (ø)
src/tool/subcommands/archive_cmd.rs	29.30% <0.00%> (ø)
src/db/parity_db/gc.rs	35.20% <66.66%> (+2.14%)	⬆️
... and 2 more

... and 13 files with indirect coverage changes

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