tests: bluetooth: ascs: make callback expectation checks more generic

The existing ASCS test callback verification functions scale poorly and are
not easily reusable across different cases.

This change introduces a more generic approach to expectation checks by
adding `expect_bt_bap_unicast_server_cb_release_called(_expected_count,
_streams)` and similar functions, improving readability and maintainability
of ASCS unit tests.

Fixes #58034

Signed-off-by: Dima Kushchevskyi <d.kushchevskyi@sirinsoftware.com>