test : add unit tests for scorePrMergeRate function

[tmdeveloper007]

Summary of What Needs to be Done:
Add unit tests for the scorePrMergeRate function in src/lib/repo-health.ts. Tests must use vitest framework and import actual source code.

Changes that Need to be Made:

• Create test using vitest describe/it/expect
• Test rate 1.0 returns 25 points
• Test rate 0.0 returns 0 points
• Test intermediate rates scale linearly

Impact that it would Provide:

• Ensures PR merge rate scoring works correctly
• Validates 0-1 rate handling

[Harsh-Codes-77]

/assign

[github-actions]

✅ Closed as completed!

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