Wrapped mq tracing in explicit tracing enabled checks

There's a tiny performance hit when tracing protos even when disabled.
Calling into the no-op builders has some costs so now we return early
if tracing disabled.

Test: Manual
Flag: android.os.perfetto_sdk_tracing_v2
Bug: 303199244
Change-Id: I8a8433a5f4c9e12ba6299d356dabe55fc4488ffe