fix: monkey-patch _ProactorBasePipeTransport to suppress warning

python < 3.10.6 has a bug on proactor-based pipe transport: when a
`_ProactorBasePipeTransport` instance is garbage-collected (usually
after the associated event loop is closed), it will raise an error.

For older versions of python, we apply the same monkey-patchin to
suppress warnings (actually these are errors).

Ref: python/cpython#83413 and python/cpython#92841

CI output (pytest warnings):

```
======================= 71 passed, 66 warnings in 6.55s =======================
 Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x0000021A9534F700>
  Traceback (most recent call last):
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\proactor_events.py", line 115, in __del__
      _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\proactor_events.py", line 79, in __repr__
      info.append(f'fd={self._sock.fileno()}')
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\windows_utils.py", line 102, in fileno
      raise ValueError("I/O operation on closed pipe")
  ValueError: I/O operation on closed pipe
  Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x0000021A9534F700>
  Traceback (most recent call last):
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\proactor_events.py", line 115, in __del__
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\proactor_events.py", line 79, in __repr__
    File "C:\hostedtoolcache\windows\Python\3.8.10\x64\lib\asyncio\windows_utils.py", line 102, in fileno
  ValueError: I/O operation on closed pipe
```

Author: wookayin

pynvim/msgpack_rpc/event_loop/asyncio.py

@@ -12,6 +12,7 @@
 import logging
 import os
 import sys
+import warnings
 from collections import deque
 from signal import Signals
 from typing import Any, Callable, Deque, List
@@ -22,15 +23,34 @@
 debug, info, warn = (logger.debug, logger.info, logger.warning,)
 
 loop_cls = asyncio.SelectorEventLoop
+
 if os.name == 'nt':
+    import msvcrt  # pylint: disable=import-error
     from asyncio.windows_utils import PipeHandle  # type: ignore[attr-defined]
-    import msvcrt
 
     # On windows use ProactorEventLoop which support pipes and is backed by the
     # more powerful IOCP facility
     # NOTE: we override in the stdio case, because it doesn't work.
     loop_cls = asyncio.ProactorEventLoop  # type: ignore[attr-defined,misc]
 
+    # Workaround for a bug in Proactor-based pipe transport:
+    # - python/cpython#83413 ("Event loop is closed") which is fixed by
+    #   python/cpython#92841 in python 3.10.6+
+    # Solution: monkey-patch _ProactorBasePipeTransport.
+    # pylint: disable=protected-access
+    if sys.version_info < (3, 10, 6):
+        from asyncio.proactor_events import _ProactorBasePipeTransport
+
+        def __del__(self):  # noqa
+            if self._sock is not None:
+                warnings.warn(f"unclosed transport {self!r}",
+                              ResourceWarning, source=self)
+                self._sock.close()
+
+        _ProactorBasePipeTransport.__del__ = __del__  # type: ignore # noqa
+        del __del__, _ProactorBasePipeTransport
+    # pylint: enable=protected-access
+
 
 class AsyncioEventLoop(BaseEventLoop, asyncio.Protocol,
                        asyncio.SubprocessProtocol):