test: add streak calculation tests for Monday-to-Friday

[abhilashgedela28-lang]

Description

Fixes streak computation test verification for custom weekday contribution patterns, ensuring no off-by-one errors when managing calendar offsets and date boundaries.
fixes #1505

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 (This is a backend unit test change and does not affect the visual presentation of the SVG).

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: add unit test for Monday-Friday exclusive commit streaks).
• 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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[abhilashgedela28-lang]

If you review this as soon as possible it will be helpful me to solve the others also. I was getting errors when performing different issues and submitting PRs of same repo. Once this is closed I will again put PR on the other two.
Thank you

[Aamod007]

Adds a Monday-Friday streak test with 4 evaluation dates: Friday (active 5-day streak), Saturday (grace keeps streak alive), Sunday (streak broken), Wednesday (mid-week streak). 55/55 tests pass.

[abhilashgedela28-lang]

So if you merge this I can able to do the others also .
Thank you

[github-actions]

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