Refactored libbt_audio_hal_hearing_aid_software_encoding_fuzzer

The following are updates to the fuzzer:
1. Coverage improvement from 6% to 42%
2. Added new APIs

Test: m libbt_audio_hal_hearing_aid_software_encoding_fuzzer
exec/sec: 1731
Bug: 326543913

Change-Id: Ia11072e279cc8082f40f61dd142ffbbb9906d0a4