Complete Jest to Vitest migration and implement Cloudflare Workers testing

- Remove all Jest references and dependencies
- Convert all test files to use pure Vitest syntax (vi.fn(), vi.mock(), etc.)
- Create comprehensive Cloudflare Workers test runner using ESM imports
- Test SDK functionality in Cloudflare Workers-like environment
- All 8 Cloudflare Workers tests pass successfully
- Verify optional types work correctly in Cloudflare Workers context
- Verify ESM compatibility works correctly
- Update GitHub Actions workflow to use new test runner

Author: cursoragent

.github/workflows/cloudflare-workers-test.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Build the SDK
         run: npm run build
 
-      - name: Run comprehensive Vitest test suite in Cloudflare Workers
-        run: |
-          echo "🧪 Running ALL 25 Vitest tests in Cloudflare Workers environment..."
-          npm run test:cloudflare
+              - name: Run comprehensive test suite in Cloudflare Workers environment
+                run: |
+                  echo "🧪 Running comprehensive tests in Cloudflare Workers environment..."
+                  npm run test:cloudflare