\test(dateRange): add empty-fallback test and robust parsing"

[ShafinNigamana]

Description

Adds a robust empty-fallback test suite for utils/dateRange.ts and refactors the formatDateRange function to safely handle missing, null, undefined, empty/whitespace, or invalid year parameters without throwing exceptions or crashing.

Fixes #4306

Pillar

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

Visual Preview

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., test(dateRange): ...).
• 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.

[Aamod-Dev]

Good work on this one. I reviewed the diff and it looks ready to go from my side.

The test coverage added here looks comprehensive and well-structured. It definitely improves the reliability of the system.

I've approved the PR. Thanks again!

[Aamod-Dev]

Thanks for the contribution. I've taken a look at the changes and everything seems to align with what we need here.

Looks solid. I'll go ahead and approve.

[github-actions]

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

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[Aamod-Dev]

Review Summary
Removed duplicate category labels (quality:exceptional, ype:feature) to adhere to the strict rule of exactly one label per category (retained quality:clean, ype:testing).