Add unit test for public methods in radio tuner

Unit tests for public methods in public abstract radio tuner are
added. Meanwhile, resistering program list callback with executor
are also tested when identifiers are removed to coverge tests for
all methods in program list callback.

Bug: 249602599
Test: atest DefaultRadioTunerTest
Change-Id: If6d6f60a8a1d4b7177ea4bbfeb97cc53b6bff4c4