Use single thread ExecutorService to process ProtoLogging

We were using a CachedThreadPool which has no upper bound on the number of threads. So if we traced a lot in a fast succession we could end up with too many thread for Perfetto to handle.

Bug: 337222696
Test: Make sure atest com.android.server.wm.flicker.launch can finish without crashing
Change-Id: I837960abcd7c159855b0da9dee709fe06a452357