This commit adds support for the Fetch API's cache and priority options when using HttpClient with the withFetch provider.

The change includes:

• Added cache and priority to the HttpRequestInit interface
• Modified FetchBackend to pass the options
• Added unit tests to validate behavior

Motivation / Use Cases

The cache and priority options are particularly useful for:

• Controlling how HTTP requests are cached (cache: 'no-store', 'reload', etc.)
• Suggesting the relative priority of resource loading to the browser (priority: 'high', 'low', 'auto')
• Improving performance metrics (e.g., LCP) by prioritizing critical assets
• Reducing unnecessary network traffic for cached resources

Proposed Solution

• Add cache and priority to the HttpRequestInit interface
• Implement property handling in the HttpRequest class
• Pass the options through FetchBackend to the native Fetch API
• Maintain full backward compatibility

Examples of New Usage

// GET request with cache and priority
http.get('/assets/hero-image.jpg', {
  cache: 'force-cache',
  priority: 'high'
}).subscribe();