typing: add type hints to cloudinit.temp_utils

[Prathamesh0901]

Proposed Commit Message

typing: add type hints to cloudinit.temp_utils

Adds type annotations to all functions in cloudinit/temp_utils.py
and removes the module from the check_untyped_defs exemption list
in pyproject.toml.

Also replaces a direct attribute assignment (fh.unlink = ...) with
setattr(), matching the existing pattern used for fh.unlink_now,
to resolve a mypy attr-defined error once strict checking applies
to this module.

Additionally adds an explicit Union[bool, str] annotation to
umount in cloudinit/util.py's mount_cb(), since correctly typing
temp_utils.tempdir()'s return value as Iterator[str] surfaced a
latent bool/str ambiguity that was previously masked by the
untyped default.

Refs GH-5445

Additional Context

Part of the ongoing effort tracked in #5445 to incrementally enable
check_untyped_defs across the codebase. This PR covers
cloudinit/temp_utils.py. The util.py change is a small, necessary
side effect (see commit message) rather than unrelated scope
creep -- happy to split it into a separate commit/PR if preferred.

No new tests added -- this is a type-only change with no
behavioral difference, verified by the existing test suite
passing unchanged.

Test Steps

.tox/mypy/bin/python -m mypy cloudinit/temp_utils.py
tox -e mypy
tox -e py3 -- tests/unittests/test_temp_utils.py
tox -e py3

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[Prathamesh0901]

please review @holmanb

[holmanb]

Thanks for this proposal. It looks like this is on track. I have a couple of minor nitpicks.

[Prathamesh0901]

Hi @holmanb, just checking in, all checks are passing now after the changes. Let me know if anything else needs changing.

[Prathamesh0901]

@holmanb I have made the changes mentioned in the last review.