Pass asyncio event loop config to `axon` to be used by `uvicorn`

[cassova]

Is your feature request related to a problem? Please describe.

Yes. When the package uvloop is installed with SN1, you get an error There is no current event loop in thread 'Thread-4 (run)'.. This occurs because uvloop overrides the asyncio loop functionality and now requires a loop to be defined within the bittensor package.

Describe the solution you'd like

I suggest passing in a loop: asyncio.LoopSetupType into the axon.__init__(...).

Describe alternatives you've considered

I see a few possible solutions:

1. hardcode axon.py to use loop="asyncio":

        self.fast_config = uvicorn.Config(
            self.app, host="0.0.0.0", port=self.config.axon.port, log_level=log_level, loop="asyncio"
        )

2. have the loop passed in when an axon is initiated:

    def __init__(
        self,
        wallet: Optional["bittensor.wallet"] = None,
        config: Optional["bittensor.config"] = None,
        port: Optional[int] = None,
        ip: Optional[str] = None,
        external_ip: Optional[str] = None,
        external_port: Optional[int] = None,
        max_workers: Optional[int] = None,
        loop: Optional[asyncio.LoopSetupType] = None,  # new parameter
    ):
 ...
        self.fast_config = uvicorn.Config(
            self.app, host="0.0.0.0", port=self.config.axon.port, log_level=log_level, loop=loop
        )

3. Find a way to attach uvicorn server to an existing event loop. This doesn't seem to be supported from what I can find. They did make this change awhile back but was later removed for reasons I haven't been able to determine. The server itself now only takes in loop of type LoopSetupType instead of the AbstractEventLoop type we'd need.

Additional context

No response

[cassova]

Something I also tried that didn't work: export UVICORN_LOOP=asyncio

I was a bit surprised this didn't work given the documentation. I suspect the reason being this comment:

CLI options and the arguments for uvicorn.run() take precedence over environment variables

[thewhaleking]

CLosed by #2679