Introduce Controller to ProtoLog

This refactor introduces a ProtoLogController class to manage ProtoLog's internal state.
This controller object encapsulates all the logic for initializing ProtoLog, managing registered groups, and maintaining the singleton instances of ProtoLog implementations.

This change improves testability by allowing unit tests to inject or replace the controller with mock/stub instances to isolate test state. It also makes it possible to have different implementations of the main logic, while having all the coordination logic inside the controller.

Flag: EXEMPT refactor
Test: atest TracingTests
Change-Id: I13198e5f5ad3f62cb730577f77b9199d4f88327e