sec: replace math/rand v1 with math/rand/v2 for rate-limiter jitter (closes #419)

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Summary

• Replaces "math/rand" (v1) with "math/rand/v2" in providers/aws/recommendations/ratelimiter.go -- the only v1 call site found in providers/, internal/, and pkg/.
• math/rand/v2 is already the project standard for non-crypto jitter (see pkg/retry/exponential.go with an explanatory comment); this aligns the rate-limiter with that convention.
• The call site (rand.Float64()) is API-identical in v2; no logic changes.

Test plan

• go build ./... passes
• go test github.com/LeanerCloud/CUDly/providers/aws/recommendations -- all 281 tests pass
• New TestWait_JitterRange: 200 iterations assert jitter stays within [0, 20%] of base delay and spans more than 5% (confirms the source is not stuck at zero)

Closes #419

Summary by CodeRabbit

• Refactor

  • Updated rate limiter's random number generation and refactored jitter calculation logic for improved maintainability.

• Tests

  • Added deterministic unit tests for rate limiter jitter computation to improve test reliability and coverage.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 04b65418-1a10-4d03-8e93-832aebcd9f9f

📥 Commits

Reviewing files that changed from the base of the PR and between 4956d66 and 840c5e5.

📒 Files selected for processing (2)

• providers/aws/recommendations/ratelimiter.go
• providers/aws/recommendations/ratelimiter_test.go

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📝 Walkthrough

Walkthrough

This PR upgrades the rate limiter's jitter system from math/rand v1 to math/rand/v2 for API consistency and extracts the jitter logic into a pure, unit-testable function. The implementation is validated by a deterministic test covering 10,000 inputs.

Changes

Rate Limiter Jitter Upgrade

Layer / File(s)	Summary
Jitter extraction and math/rand/v2 upgrade providers/aws/recommendations/ratelimiter.go	Import math/rand/v2, extract inline jitter computation into a pure computeJitter(delay, r) helper that computes up to 20% of delay as jitter, and update Wait to call the helper with rand.Float64().
Deterministic jitter unit test providers/aws/recommendations/ratelimiter_test.go	Add TestComputeJitter to verify the helper function directly across 10,000 evenly spaced uniform inputs, ensuring jitter bounds are honored and max spread reaches at least 95% of limit.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A limiter hops with jitter anew,
From rand v1 to v2 so true,
Pure function extracted, no sleeps in sight,
Ten thousand tests verify it's right! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly and concisely describes the main change: replacing math/rand v1 with math/rand/v2 in the rate-limiter jitter implementation, which is the core focus of this changeset.
Linked Issues check	✅ Passed	The PR fully addresses issue #419 by replacing math/rand v1 with math/rand/v2 in ratelimiter.go, updating jitter logic with extracted helper function, and adding deterministic unit tests that validate jitter bounds without wall-clock timing.
Out of Scope Changes check	✅ Passed	All changes are narrowly scoped to address issue #419: import replacement, jitter refactoring with extracted helper, and deterministic test addition; no unrelated modifications are present.

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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 fix/419-wave16

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