bug-fix: Protect acquiring buffer by different workers

[msluszniak]

Description

This PR tries to fix the random BAD_ACCESS error in speech to text. After streaming a while to a model, there was a crash. I suspect that it was generated by the following. When incrementally adding chunks, model has latency and the buffer increases. So it sometimes reallocates to a different part in memory. Function that processes audio and passes it to executorch runtime does not know about reallocation and passes old memory address. When executorch runtime tries to copy the memory now the address is invalid.

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

I run 30 minutes of live transcription on iOS and do not observe the crash. You can check this similar way.

Screenshots

Related issues

Closes #791

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes