test(calculate): verify streak formulas for multiple weeks gaps timeline (Variation 3) (JhaSourav07#1489) (JhaSourav07#1906)

## Description

This PR adds test coverage to verify the streak formulas when there are
multiple weeks of zero contribution gaps between active streaks, acting
as Variation 3 of the multiple weeks gaps timeline tests.

Fixes JhaSourav07#1489

## Pillar

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

## Visual Preview

N/A (Tests only)

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=boss477`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [x] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have starred the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/calculate.test.ts

@@ -517,6 +517,72 @@ describe('calculateStreak', () => {
     expect(result.currentStreak).toBe(15);
     expect(result.longestStreak).toBe(15);
   });
+
+  it('verify streak formulas for multiple weeks gaps timeline (Variation 3)', () => {
+    // Streak 1: 5 days
+    // Gap 1: 14 days (2 weeks of zeros)
+    // Streak 2: 10 days (longest)
+    // Gap 2: 21 days (3 weeks of zeros)
+    // Streak 3: 3 days (current) ending on the last day
+    const calendar = buildCalendar([
+      1,
+      1,
+      1,
+      1,
+      1, // Streak 1 (5 days)
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0, // Gap 1 (14 days)
+      1,
+      1,
+      1,
+      1,
+      1,
+      1,
+      1,
+      1,
+      1,
+      1, // Streak 2 (10 days)
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0,
+      0, // Gap 2 (21 days)
+      1,
+      1,
+      1, // Streak 3 (3 days - ending on last day)
+    ]);
+    const result = calculateStreak(calendar);
+    expect(result.longestStreak).toBe(10);
+    expect(result.currentStreak).toBe(3);
+  });
 });
 
 it('handles massive single-day commit spike timeline', () => {