Unmaintained flake8-noqa, Adding support for external codes

[Avasam]

About a year ago, I opened a PR to add support recognizing external codes to flake8-noqa, complete with unit tests (plinss/flake8-noqa#30), to achieve the same feature as

typeshed/pyproject.toml

Lines 36 to 38 in e5c5318

	# We still use flake8-pyi and flake8-noqa to check these (see .flake8 config file);
	# tell ruff not to flag these as e.g. "unused noqa comments"
	external = ["F821", "NQA", "Y"]

with the goal of addressing this issue:

typeshed/pyproject.toml

Lines 49 to 51 in e5c5318

	# PYI: only enable rules that have autofixes and that we always want to fix (even manually),
	# avoids duplicate # noqa with flake8-pyi and flake8-noqa flagging `PYI` codes
	# See https://github.com/plinss/flake8-noqa/issues/22

However, here we are, a year later, with no news from the maintainer despite some attempts at contacting outside GitHub through official email. Peter Linss is still active at w3ctag, leaving me under the impression that the project is currently unmaintained, and wondering if we could instead use a fork based on the feature I added. Either by pointing at a GitHub branch or release in our requirements file, or by publishing a fork on PyPI under the python/typeshed or PyCQA umbrella.

[srittau]

I'm fine with removing flake8-noqa from typeshed.