test: add unit tests for rate-limit.ts (#2760)

[ANU5565]

Summary

This PR adds essential unit tests for src/lib/rate-limit.ts to ensure robust IP detection and rate-limiting functionality.

Closes #

This closes #2760.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• Created test/rate-limit.test.ts.

• Added test cases for getClientIp including headers (cf-connecting-ip, x-real-ip, x-forwarded-for) and priority handling.

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How to Test

1. Run npm install to ensure dependencies are up to date.

2. Run npx vitest test/rate-limit.test.ts to execute the new tests.

3. Verify that all tests pass.

Expected result:
All tests in rate-limit.test.ts should pass with green status

Screenshots / Recordings

Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

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Accessibility (UI changes only)

• Keyboard navigation works correctly
• Color contrast meets WCAG AA standard
• ARIA labels / roles added where needed
• Tested on mobile / responsive layout

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Additional Context

[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]

Merge.

[Priyanshu-byte-coder]

Closing. #2733 was selected as the best rate-limit test suite — it covers all fallback headers and the full logic including pruning. This PR only has a single test for one header. Thanks for contributing!