fix: Ensure subprocess is killed on linux

[LordOfPolls]

What type of pull request is this?

• Non-breaking code change
• Breaking code change
• Documentation change/addition
• Tests change

Description

On Linux the Audio subproccess was not exiting successfully, resulting in zombie processes being left behind. This should resolve this, without impacting Windows.

I also found that the read_ahead task was not being cancelled either, this fixes that too.

Changes

• Set subprocess stdin to DEVNULL
• Check if child process is runnning in _read_ahead
• Add check for child process state in cleanup

Checklist

• I've formatted my code with Black
• I've ensured my code works on Python 3.10.x
• I've tested my code

[LordOfPolls]

Unless there are any objections this PR will be merged. My tests shows it resolves the aforementioned issue