bpo-46417: Clear _io module static objects at exit

[vstinner]

Add _PyIO_Fini() function, called by finalize_interp_clear(). It
clears static objects used by the _io extension module.

https://bugs.python.org/issue46417

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x has failed when building commit 9c8e490.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/725/builds/813) and take a look at the build logs.
4. Check if the failure is related to this commit (9c8e490) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/725/builds/813

Summary of the results of the build (if available):

== Tests result: ENV CHANGED ==

411 tests OK.

10 slowest tests:

• test_concurrent_futures: 3 min 47 sec
• test_multiprocessing_spawn: 2 min 30 sec
• test_multiprocessing_forkserver: 1 min 47 sec
• test_unparse: 1 min 26 sec
• test_asyncio: 1 min 17 sec
• test_tokenize: 1 min 15 sec
• test_logging: 55.9 sec
• test_capi: 53.5 sec
• test_lib2to3: 52.3 sec
• test_ssl: 48.9 sec

1 test altered the execution environment:
test_ftplib

17 tests skipped:
test_dbm_gnu test_devpoll test_epoll test_gdb test_ioctl
test_msilib test_multiprocessing_fork test_ossaudiodev test_spwd
test_startfile test_tix test_tk test_ttk_guionly test_winconsoleio
test_winreg test_winsound test_zipfile64

Total duration: 8 min 35 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncore.py", line 90, in read
    obj.handle_read_event()
    ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_ftplib.py", line 384, in handle_read_event
    self._do_ssl_handshake()
    ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_ftplib.py", line 345, in _do_ssl_handshake
    self.socket.do_handshake()
    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/ssl.py", line 1345, in do_handshake
    self._sslobj.do_handshake()
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
ssl.SSLZeroReturnError: TLS/SSL connection has been closed (EOF) (_ssl.c:998)


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/multiprocessing/resource_tracker.py", line 209, in main
    cache[rtype].remove(name)
    ^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '/psm_9434db3d'


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/multiprocessing/resource_tracker.py", line 209, in main
    cache[rtype].remove(name)
    ^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '/psm_10d267bb'


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/threading.py", line 1031, in _bootstrap_inner
    self.run()
    ^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_ftplib.py", line 298, in run
    asyncore.loop(timeout=0.1, count=1)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncore.py", line 214, in loop
    poll_fun(timeout, map)
    ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncore.py", line 157, in poll
    read(obj)
    ^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncore.py", line 94, in read
    obj.handle_error()
    ^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_ftplib.py", line 421, in handle_error
    raise Exception
    ^^^^^^^^^^^^^^^
Exception
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