test: add comprehensive unit tests for streak calculation utilities

[Shanidhya01]

Summary

Adds comprehensive unit tests for streak calculation utility functions to improve reliability and prevent regressions in DevTrack's streak tracking system.

Closes #1069

Changes Made

• Added unit tests for current streak calculation
• Added unit tests for longest streak calculation
• Added unit tests for streak-at-risk detection
• Added tests for streak reset behavior
• Added tests for empty commit history
• Added tests for date boundary edge cases
• Added tests for leap year handling
• Added tests for month transitions (28/29/30/31 days)
• Added tests for timezone-related scenarios
• Added tests for commits made after midnight

Test Coverage

Covered scenarios:

• Returns 0 for empty commit history
• Counts consecutive days correctly
• Resets streak on missed day
• Handles streak freeze functionality (if implemented)
• Calculates longest streak accurately
• Detects streak at risk when no commit exists today
• Handles timezone boundaries correctly
• Counts today correctly for post-midnight commits
• Handles leap year dates (Feb 29)
• Handles month length variations

Type of Change

• Test addition
• Bug fix
• New feature
• Breaking change

Checklist

• Tests added
• Existing tests pass
• No production behavior changed
• Code follows project conventions

[github-actions]

GSSoC Label Checklist 🏷️

@Umbrella-io — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Legit-Ox]

Test coverage is solid — good edge case variety across leap years, month transitions, timezone boundaries, and freeze dates. Three issues before merging:

1. rolldown added to production dependencies — unrelated to this PR and shouldn't be there at all
2. One test name directly contradicts its assertion
3. package-lock.json accidentally narrows the Node engine range

[Shanidhya01]

Ok will fix it by the end of the day

[Priyanshu-byte-coder]

The test coverage here is genuinely strong — the timezone edge cases, leap year handling, and streak-utils coverage are valuable. A few things to fix before merge:

1. Remove the package.json change — changing engines from 20.x to >=20.0.0 is unrelated to tests and belongs in a separate PR.

2. package-lock.json changes — the added resolved/integrity fields for rolldown are also unrelated. Please drop these.

3. File conflict with test : added unit tests for streak.ts #2776 — both PRs create test/streak.test.ts. Since test : added unit tests for streak.ts #2776 has already been merged, please either rename your file (e.g. test/streak-comprehensive.test.ts) or consolidate the tests into the existing file to avoid conflicts.

Fix these and the test quality is solid enough to merge.