Fix test_lazy_choices_help failing on Python 3.14

[vtino17]

Fixes #1641

Problem

Python 3.14 validates an argparse action's help immediately after constructing the action. That eager read caused LazyChoices.help to load choices during parser initialization, breaking the lazy contract.

Change

• detect argparse's new _check_help validation path
• skip exactly the initial eager help read
• preserve normal lazy help generation when help is actually rendered

Validation

Tested with Python 3.14.6:

• parser initialization does not call the choices getter
• parser initialization does not call the help formatter
• rendering help calls the formatter once with the loaded choices
• code-style check: pass

[vtino17]

I corrected the Python 3.14 fix in commit 0685ac0. Python 3.14 validates action help after the action constructor returns, so initializing _help before super() was insufficient. The updated implementation skips exactly that initial eager validation when _check_help exists, while preserving lazy help generation. The existing regression expectations now pass under Python 3.14.6: neither the choices getter nor help formatter is called during parser initialization, and help rendering still calls the formatter once.