gh-101100: Fix Sphinx warnings in library/cmd.rst

[hugovk]

Fix 13 Sphinx warnings:

• do_foo, complete_foo, help_bar and do_bar, do_forward and do_playback are examples, silence with !
• There's already a paragraph about do_help, let's add .. method:: Cmd.do_help(arg) so it can be linked to
• Silence sys.stdout.write and sys.stdin.readline with !. Or is there somewhere good to link to?
• cmdqueue was missing the class ref, change to ~Cmd.cmdqueue

Doc/library/cmd.rst:78: WARNING: py:meth reference target not found: do_foo
Doc/library/cmd.rst:78: WARNING: py:meth reference target not found: do_help
Doc/library/cmd.rst:78: WARNING: py:meth reference target not found: do_shell
Doc/library/cmd.rst:88: WARNING: py:meth reference target not found: complete_foo
Doc/library/cmd.rst:96: WARNING: py:meth reference target not found: do_help
Doc/library/cmd.rst:96: WARNING: py:meth reference target not found: help_bar
Doc/library/cmd.rst:96: WARNING: py:meth reference target not found: do_bar
Doc/library/cmd.rst:96: WARNING: py:meth reference target not found: do_help
Doc/library/cmd.rst:231: WARNING: py:meth reference target not found: sys.stdout.write
Doc/library/cmd.rst:231: WARNING: py:meth reference target not found: sys.stdin.readline
Doc/library/cmd.rst:251: WARNING: py:meth reference target not found: do_forward
Doc/library/cmd.rst:256: WARNING: py:meth reference target not found: do_playback
Doc/library/cmd.rst:256: WARNING: py:attr reference target not found: cmdqueue

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--113502.org.readthedocs.build/

[serhiy-storchaka]

LGTM. I have only doubts about silencing sys.stdout.write and sys.stdin.readline. Maybe add references to sys.stdout and sys.stdin?

[hugovk]

Sounds good, updated!

[AlexWaygood]

Nitpick: no need to link to the thing we're already reading (otherwise, this looks great!)

[AlexWaygood]

LGTM!

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 4acf825058a7785ed3d66d4f5a4991298c011f64 3.12

[bedevere-app]

GH-113510 is a backport of this pull request to the 3.11 branch.

[bedevere-app]

GH-113511 is a backport of this pull request to the 3.12 branch.