Add python 3.10 support

[augray]

It would be nice to have support for the latest stable python version. We currently have some libraries that aren't playing well on 3.10 (I think eventlet, perhaps?).

[bobek]

That would be awesome. Currently it crashes with

  File "/tmp/virtualenv/bin/sematic", line 5, in <module>
    from sematic.cli.main import cli
  File "/tmp/virtualenv/lib/python3.10/site-packages/sematic/cli/main.py", line 3, in <module>
    import sematic.cli.start  # noqa: F401
  File "/tmp/virtualenv/lib/python3.10/site-packages/sematic/cli/start.py", line 16, in <module>
    from sematic.api.server import run_wsgi
  File "/tmp/virtualenv/lib/python3.10/site-packages/sematic/api/server.py", line 8, in <module>
    from flask_socketio import SocketIO, Namespace  # type: ignore
  File "/tmp/virtualenv/lib/python3.10/site-packages/flask_socketio/__init__.py", line 9, in <module>
    from socketio import socketio_manage  # noqa: F401
  File "/tmp/virtualenv/lib/python3.10/site-packages/socketio/__init__.py", line 9, in <module>
    from .zmq_manager import ZmqManager
  File "/tmp/virtualenv/lib/python3.10/site-packages/socketio/zmq_manager.py", line 5, in <module>
    import eventlet.green.zmq as zmq
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/__init__.py", line 17, in <module>
    from eventlet import convenience
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/convenience.py", line 7, in <module>
    from eventlet.green import socket
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/green/socket.py", line 4, in <module>
    __import__('eventlet.green._socket_nodns')
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/green/_socket_nodns.py", line 11, in <module>
    from eventlet import greenio
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/greenio/__init__.py", line 3, in <module>
    from eventlet.greenio.base import *  # noqa
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/greenio/base.py", line 32, in <module>
    socket_timeout = eventlet.timeout.wrap_is_timeout(socket.timeout)
  File "/tmp/virtualenv/lib/python3.10/site-packages/eventlet/timeout.py", line 166, in wrap_is_timeout
    base.is_timeout = property(lambda _: True)
TypeError: cannot set 'is_timeout' attribute of immutable type 'TimeoutError'

[augray]

Great, thanks for capturing the trace here!