airflowctl: Fix datetime.datetime CLI parameter parsing

[guptakushal03]

Fixes datetime.datetime-typed CLI parameter parsing in airflowctl.

Previously, datetime.datetime parameters were mapped directly to the datetime.datetime constructor, causing valid ISO-8601 datetime strings (for example, 2026-07-01 and 2026-07-01T14:30:00) to be rejected by argparse.

This change:

• Adds iso_datetime_type() to parse ISO-8601 datetime strings using datetime.datetime.fromisoformat().
• Updates datetime.datetime-typed CLI arguments to use the parser instead of the bare constructor.
• Adds unit tests covering valid datetime inputs and invalid values that should raise argparse.ArgumentTypeError.

closes: #70232

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Important

🛠️ Maintainer triage note for @guptakushal03 · by @potiuk · 2026-08-13 12:55 UTC

Helpful heads-up from the maintainers — please address before this PR can be reviewed:

• ❌ Merge conflicts. See docs.
• ❌ Pre-commit / static checks. See docs.

Full list of what we check: Pull Request quality criteria.

The ball is in your court — you've been assigned to this PR. Fix the above, then mark it Ready for review.

_{Automated triage — may be imperfect; a maintainer takes the next look.}

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