Add Unit Tests for GitHub Username Validation

[Rakshak05]

Description

Fixes #8368

Added a dedicated unit test file lib/validations.github-username.test.ts to provide comprehensive test coverage for validateGitHubUsername.

Tests cover:

• Valid usernames (simple, hyphenated, numeric, mixed-case, max length of 39 chars)
• Invalid usernames (empty, null, undefined, non-string types, special characters, leading/trailing hyphens, consecutive hyphens, exceeding length limit, spaces, underscores)
• Real GitHub usernames for positive cases

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

N/A (Unit tests only)

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (localhost:3000/api/streak?user=YOUR_USERNAME).
• I have run npm run format and npm run lint locally and resolved all errors (CI will fail otherwise).
• My commits follow the Conventional Commits format (e.g., feat(themes): ..., fix(calculate): ...).
• I have updated README.md if I added a new theme or URL parameter.
• I have started the repo.
• I have made sure that i have only one commit to merge in this PR.
• The SVG output matches the CommitPulse "premium quality" aesthetic standard (no raw elements, smooth animations, correct fonts).
• (Recommended) I joined the CommitPulse Discord community for contributor discussions, mentorship, and faster PR support.

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[retenta-bot]

This PR enhances the testing coverage for username validation, which is crucial for maintaining data integrity and user experience. It aligns with previous decisions to improve username normalization across various APIs. Thank you for your contribution!

[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	5004.32 KB	5004.32 KB	0 B
Total CSS	354.80 KB	354.80 KB	0 B

[Aamod007]

Very comprehensive test suite for GitHub username validation! The negative cases are well thought out and perfectly ensure that our security and length validations won't regress. Approved!

[github-actions]

🎉 Congratulations @Rakshak05! Your PR has been successfully merged. 🚀

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