Allow disabling the bellows UART thread

[puddly]

Not all environments support or need threading, namely https://pyscript.net/ and command line applications:

zha:
  zigpy_config:
    use_thread: false

Once some hard-to-reproduce, low-level bugs are ironed out of the bellows asyncio thread, I think it would be beneficial to move it into zigpy.

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (899218a) compared to base (3340e12). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

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[pipiche38]

What do you recommend ? I see that the default is to use the thread. In fact what is the benefit to use it ?

[puddly]

In fact what is the benefit to use it ?

There's no reason not to use it. If your event loop is busy or has stuttering, it will break EZSP communication with the radio. The only reason I'm adding this option is to allow bellows to be used in environments where threading is not implemented.