Make airflow --help run five times quicker

[ashb]

Importing anything from airflow.models pulls in a lot of airflow, so
delay imports until the functions are called, or make use of the
TYPE_CHECKING to not actually import at runtime.

Before: mean 2.58s (with a lot of variance)

airflow ❯ for i in 1 2 3; do time airflow --help >/dev/null; done
airflow --help > /dev/null  2.00s user 1.39s system 176% cpu 1.928 total
airflow --help > /dev/null  2.84s user 1.43s system 151% cpu 2.817 total
airflow --help > /dev/null  3.00s user 1.37s system 145% cpu 3.009 total

After: 0.526s

airflow --help > /dev/null  0.39s user 0.04s system 99% cpu 0.435 total
airflow --help > /dev/null  0.40s user 0.05s system 99% cpu 0.446 total
airflow --help > /dev/null  0.64s user 0.05s system 99% cpu 0.698 total

This also has an advantage in development where a syntax error doesn't
fail with a slightly confusing error message about "unable to configure
logger 'task'".

---

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[ashb]

Discovered with

python -X importtime -m airflow version 2>import-trace.log

And then tuna import-trace.log

Before

After

[ryw]

watched you code this live :)

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[potiuk]

I'd prefer to solve it differently, but pragmatically, this is easiest way now.

[ashb]

I'd prefer to solve it differently, but pragmatically, this is easiest way now.

I would also like that importing modules had less "side-effects", but...

I think we need both ways -- because fundamentally, even if importing from models imported less code, there's still the fact that in some cases we are only importing it for a type annotation, which is just wasteful at runtime