* - Added `NativeLogConfig` which allows overriding the llama.cpp log callback
 - Delaying binding of this into llama.cpp until after `NativeLibraryConfig` has loaded

* Using the log callback to show loading log messages during loading.

* Registering log callbacks before any calls to llama.cpp except `llama_empty_call`, this is specifically selected to be a method that does nothing and is just there for triggering DLL loading.

* - Removed much of the complexity of logging from `NativeApi.Load`. It always call whatever log callbacks you have registered.
 - Removed alternative path for `ILogger` in NativeLibraryConfig, instead it redirects to wrapping it in a delegate.

* Saving a GC handle to keep the log callback alive

* Removed prefix, logger should already do that.

* Buffering up messages until a newline is encountered before passing log message to ILogger.

* - Added trailing `\n` to log messages from loading.
 - Using `ThreadLocal<StringBuilder>` to ensure messages from separate threads don't get mixed together.