test(cache): verify multidimensional array values (JhaSourav07#2033)

## Description

Fixes JhaSourav07#1396

Adds a test verifying that `TTLCache` correctly stores and retrieves
complex multidimensional array values. The test ensures nested array
structures are preserved exactly when fetched from the cache.

## 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 (test-only change)

## Checklist before requesting a review:

* [x] I have read the `CONTRIBUTING.md` file.
* [x] I have tested these changes locally (`npm run test --
lib/cache.test.ts`).
* [ ] 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): ...`).
* [ ] I have updated `README.md` if I added a new theme or URL
parameter.
* [x] I have started the repo.
* [x] 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 (not applicable — test-only change).
* [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/cache.test.ts

@@ -409,11 +409,15 @@ describe('TTLCache', () => {
       const matrix = [
         [1, 2],
         [3, 4],
+        [5, 6],
       ];
 
       cache.set('matrix', matrix, 60_000);
 
-      expect(cache.get('matrix')).toEqual(matrix);
+      const cached = cache.get('matrix');
+
+      expect(cached).toEqual(matrix);
+      expect(cached?.[2]?.[1]).toBe(6);
 
       cache.destroy();
     });