bass_client: Add intentional and unintentional device disconnection tests

This change adds test of unintentional and intentional disconnection in
broadcast and broadcast assistant context.

Tag: #feature
Bug: 322332749
Bug: 308171251
Test: atest BassClientServiceTest
Change-Id: I59bfb0778a7ac8a8be9f4cd1ea534837a735e670