BassClientServiceTest: Mechanical refactor

- add helper functions to reduce the lines of code
- remove timeouts to reduce overall time of tests execution
- add new way of controlling BassClientService timeouts
- prepareConnectedDeviceGroup by default creates one place
for broadcast source addition
- remove unnecessary testDevice creation
- create global mInOrderMethodProxy
- change deprecated enableFlags/disableFlags to new
@EnableFlags/@DisableFlags annotations
- change assertThat to expect on serial checks at the end of a tests

Bug: 355218881
Flag: Exempt, tests changes only
Test: atest BassClientServiceTest
Change-Id: I8afe8e09bcc9c5328c8cf2b57c89341b0ff074ef