test : added unit tests for repoAnalyticsUtils date formatters

[tmdeveloper007]

Refs #1275.

Summary of What Has Been Done:
Added comprehensive unit tests for the date formatting utilities in src/lib/repoAnalyticsUtils.ts: formatDate, formatRelativeDate, and formatDisplayDate.

Changes Made:

• Created new test file: test/repoAnalyticsUtils.test.ts
• Added tests for formatDate covering standard dates, leap year dates, and invalid date handling
• Added tests for formatRelativeDate covering Today, Yesterday, and recent dates
• Added tests for formatDisplayDate covering string and Date object inputs

Impact it Made:
Improved test coverage for date formatting utilities used in repository analytics display. All 8 tests pass.

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GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:critical — 80 pts

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