typing: add type hints to cloudinit.distros.parsers.resolv_conf

[GoUrAv-MaLiK]

Enables check_untyped_defs for cloudinit.distros.parsers.resolv_conf by annotating ResolvConf and removing it from the mypy override list in pyproject.toml.

self._contents is Optional; it is now narrowed with an assert after parse() before it is iterated or appended to. Behaviour is unchanged.

Refs GH-5445

• I have signed the CLA
• I have included a comprehensive commit message
• I have added unit tests — N/A: typing-e class is already covered bytests/unittests/distros/test_resolv.py
• I have kept the change small
• I have added a reference to the related issue (Refs [enhancement]: fix typing of untyped-defs #5445)
• I have updated the documentation — N/A

Proposed Commit Message

typing: add type hints to cloudinit.distros.

Annotate ResolvConf and enable check_untyped
removing it from the mypy override list in pyproject.toml.

self._contents is Optional; it is now narrowed with an assert after
parse() before it is iterated or appended to

Refs GH-5445

Additional Context

Part of the incremental effort in GH-5445 tomodule-by-module.

Test Steps

tox -e mypy    # clean (270 files, --platfor
tox -e py3 -- tests/unittests/distros/test_resolv.py tests/unittests/config/test_cc_resolv_conf.py   # 30 passed
tox -e ruff && tox -e black && tox -e isort

Merge type

• Squash merge using "Proposed Commit Me

[holmanb]

While this technically is a form of type narrowing, it results in an exception when the assertion is fails.