leaudio: Fix handling stream switch between LeAudio groups

This patch fixes invalid stream switch between LeAudio devices.
Main issue was to manage common resources like
audio_sender/receiver_state_ and coresponding AudioHal calls.

Bug: 382746797
Flag: Exempt, regression tested with unit tests
Test: atest bluetooth_le_audio_client_test
Change-Id: I5935eab325816170eb74770eb02aed6bb217f4b6