Refactor Calculate Module: Document DaysInYear Export for Reuse

[tmdeveloper007]

Summary of What Has Been Done

This PR addresses issue #8337.

See the corresponding issue for full details.

Closes #8337

Note: Please assign this PR to the tmdeveloper007 account.

[retenta-bot]

This pull request improves the documentation of the daysInYear export, which will aid in its reuse across the codebase. It's important to ensure that such changes are well-documented to maintain code quality and usability. This aligns with our previous decision to fix dead code in the calculate functions, emphasizing the importance of clarity and functionality in our calculations. Thank you for your contribution, and I look forward to your updates!

[github-actions]

📦 Next.js Bundle Size Report (Gzipped Sizes)

✨ No significant bundle size changes detected.

📊 Summary of Totals

Category	PR Size	Base Size	Difference
Total JS	4052.50 KB	4052.50 KB	0 B
Total CSS	338.94 KB	338.94 KB	0 B

[Aamod007]

Adding export + JSDoc to daysInYear for reuse. Clean change. CI is failing — please fix.

Labels: level:beginner, quality:clean, type:docs, type:refactor, mentor:Aamod007

[Aamod007]

Re-reviewing after noting the only CI failure is Vercel authorization (not code-related). All other checks (Format · Lint · Typecheck · Test, Production Build, CodeQL) pass. Approving — the Vercel deploy auth is a repo-level config issue, not a code problem.