feat: add deleteCache() to purge cache without sending a request

[jornicornelese]

Summary

Currently, invalidateCache() only takes effect inside CacheMiddleware, meaning the cache is only refreshed when a request is actually sent. There's no way to just delete a cached response without making an API call.

In my own application I ran into redundant API calls — I only wanted to invalidate the cache, not immediately retrieve fresh data. This PR adds a deleteCache() method to the HasCaching trait that deletes the cached response directly, without going through the middleware pipeline.

Usage

// From the request
$request = new GetUserRequest($id);
$request->deleteCache($connector);

// From the connector
$connector->deleteCache(new GetUserRequest($id));

Changes

• Added deleteCache(Connector|Request $counterpart) to HasCaching
• Builds the same cache key as CacheMiddleware (including custom cacheKey() overrides)
• Calls Driver::delete() directly — no existing code modified
• 5 new Pest tests