Consider overriding FetchSource for pmtiles handlers

[ramSeraph]

This might be required depending on #41 . If there is a problem with the cloudflare caching.. we might need to make sure to set the appropriate headers to make sure cloudflare caching is disabled for the HEAD and GET Range requests.

[ramSeraph]

This might also be required to make sure that temporary failures in loading remote pmtiles metadata don't get cached.