- Removed the unused `appID` property from `GACAppCheckAPIService`.
- Removed heartbeat logging tests from `GACAppCheckAPIServiceTests`.
- Added request hook, additional headers and API key tests to `GACAppCheckAPIServiceTests`.
Removed the GACAppCheckProviderFactory protocol, and classes conforming to it, since they are no longer used in the non-Firebase-specific App Check SDK.
Removed the direct dependency on FIRHeartbeatLoggerProtocol from GACAppCheckAPIService, moving it up into the App Check providers.
Added request hooks (blocks) to allow heartbeat logging headers to be added to requests before they are sent.
Added logging macros as drop-in replacements for the GAC/FIRAppCheckLogger macros. These are simple wrappers around NSLog and are not compiled out based on the desired logging level.