Use single PerfettoProtoLogImpl for all tests

This ensures we don't register the data source on every test. We cannot unregister a registered datasource so the datasources just pile up and at some point leads to issues with not getting the on start callbacks in time when there are too many datasources.

Test: atest InternalTests:com.android.internal.protolog.PerfettoProtoLogImplTest
Bug: 364255103
Flag: TEST_ONLY
Change-Id: Ib0d2f733fa2ca68a744a318dd63cc007af9a9304