test: add cacheKey unit tests (JhaSourav07#566)

## Description
- exported cacheKey function
- added unit tests for cacheKey
- tested with and without year
- tested lowercase conversion
- tested all three kind values
- 
Fixes JhaSourav07#364 

## Pillar

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

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- [x] I have tested these changes locally
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resolved all errors (CI will fail otherwise).
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Author: deepsikha-dash

lib/github.test.ts

@@ -9,7 +9,7 @@ import {
   clearGitHubApiCacheForTests,
   GITHUB_CACHE_TTL_MS,
   validateGitHubUsername,
-  fetchWithRetry,
+  cacheKey,
 } from './github';
 import type { ContributionCalendar } from '../types';
 
@@ -536,73 +536,29 @@ describe('validateGitHubUsername', () => {
     expect(validateGitHubUsername('in--valid')).toBe(false);
   });
 });
-describe('fetchWithRetry', () => {
-  beforeEach(() => {
-    vi.spyOn(global, 'fetch');
-  });
 
-  afterEach(() => {
-    vi.restoreAllMocks();
+describe('cacheKey', () => {
+  it('creates key without year', () => {
+    expect(cacheKey('profile', 'DeepSikha')).toBe('profile:deepsikha');
   });
 
-  it('resolves immediately on first attempt when fetch returns 200', async () => {
-    vi.mocked(fetch).mockResolvedValueOnce(mockResponse({ ok: true }, 200));
-
-    const res = await fetchWithRetry('https://api.github.com/rest', {});
-
-    expect(res.status).toBe(200);
-    expect(fetch).toHaveBeenCalledTimes(1);
+  it('creates key with year', () => {
+    expect(cacheKey('contributions', 'DeepSikha', '2025')).toBe('contributions:deepsikha:2025');
   });
 
-  it('retries once on 429 (rate limit) and resolves on second attempt', async () => {
-    vi.useFakeTimers();
-    vi.mocked(fetch)
-      .mockResolvedValueOnce(mockResponse({}, 429))
-      .mockResolvedValueOnce(mockResponse({}, 200));
-
-    const promise = fetchWithRetry('https://api.github.com/rest', {});
-    await vi.runAllTimersAsync();
-    const res = await promise;
-
-    expect(res.status).toBe(200);
-    expect(fetch).toHaveBeenCalledTimes(2);
-    vi.useRealTimers();
+  it('converts username to lowercase', () => {
+    expect(cacheKey('repos', 'DeEpSiKhA')).toBe('repos:deepsikha');
   });
 
-  it('retries once on 500 (server error) and resolves on second attempt', async () => {
-    vi.useFakeTimers();
-    vi.mocked(fetch)
-      .mockResolvedValueOnce(mockResponse({}, 500))
-      .mockResolvedValueOnce(mockResponse({}, 200));
-
-    const promise = fetchWithRetry('https://api.github.com/rest', {});
-    await vi.runAllTimersAsync();
-    const res = await promise;
-
-    expect(res.status).toBe(200);
-    expect(fetch).toHaveBeenCalledTimes(2);
-    vi.useRealTimers();
+  it('supports profile kind', () => {
+    expect(cacheKey('profile', 'testuser')).toContain('profile');
   });
 
-  it('returns the bad response after exhausting all retries on 429', async () => {
-    vi.useFakeTimers();
-    vi.mocked(fetch).mockResolvedValue(mockResponse({}, 429));
-
-    const promise = fetchWithRetry('https://api.github.com/rest', {});
-    await vi.runAllTimersAsync();
-    const res = await promise;
-
-    expect(res.status).toBe(429);
-    vi.useRealTimers();
+  it('supports repos kind', () => {
+    expect(cacheKey('repos', 'testuser')).toContain('repos');
   });
 
-  it('propagates network error after exhausting all retries', async () => {
-    // Use real timers so retry delays actually fire and resolve cleanly
-    vi.useRealTimers();
-    vi.mocked(fetch).mockRejectedValue(new Error('network failure'));
-
-    await expect(fetchWithRetry('https://api.github.com/rest', {})).rejects.toThrow(
-      'network failure'
-    );
+  it('supports contributions kind', () => {
+    expect(cacheKey('contributions', 'testuser')).toContain('contributions');
   });
 });

lib/github.ts

@@ -129,7 +129,7 @@ const contributionsCache = new TTLCache<ContributionCalendar>(MAX_CONTRIBUTIONS_
 const profileCache = new TTLCache<GitHubUserProfile>(MAX_PROFILE_CACHE_SIZE);
 const reposCache = new TTLCache<GitHubRepo[]>(MAX_REPOS_CACHE_SIZE);
 
-function cacheKey(
+export function cacheKey(
   kind: 'contributions' | 'profile' | 'repos',
   username: string,
   year?: string