tests still rely on the removed stdlib modules asyncore/asynchat

[arhadthedev]

Reference: PEP 594 – Removing dead batteries from the standard library.

This issue tracks removal of the following modules:

• Demote from the public API into the test helpers
  • smtpd (gh-93243: Make smtpd private before porting its users #93246)
  • asynchat and asyncore (gh-72719: Remove deprecated asyncore and asynchat modules #96580)
• Port tests onto relevant analogs, step by step
  • smtpd
    • test.test_smtplib
  • asynchat and asyncore
    • test.test_ftplib
    • test.test_logging
    • test.test_poplib
      • try to give priority for bpo-30514: test_pop3lib asyncore with asyncio #1864
    • test.test_smtplib
    • test.test_ssl
    • test.libregrtest.save_env
• Remove the remnescants
  • Lib/test/smtpd.py, PCbuild/*
  • Lib/test/support/async(hat|ore).py, PCbuild/*
  • Dead links from What's New and release notes

Related issues:

• Remove asyncore, asynchat and smtpd modules #72719 (created 3 years before PEP 594 was written)
• Update tests from asyncore to asyncio #91171 (I lost authorship there during the porting from the bugs.python.org)

[JelleZijlstra]

This requires finishing #1864 (which I need to get back to).

[arhadthedev]

Asyncore-based test servers from test_ftp and test_logging cannot be ported to asyncio, the tested clients are blocking. However, instead of writing a server thread class from scratch, it would be nice to reuse test.support.threading_helper.Server from gh-92475.