gh-15770: Use TypeForm in __class_getitem__ signatures

[Andrew5057]

Addresses #15770.

TypeForm has been accepted for 3.15. When major type checkers adopt stable support for it (mypy is the most important holdout right now), we can hopefully start using it throughout the standard library to reject invalid parameterizations.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

static-frame (https://github.com/static-frame/static-frame)
+ static_frame/core/type_clinic.py:786: error: Argument 1 to "__class_getitem__" of "tuple" has incompatible type "tuple[Any, ...]"; expected "TypeForm[Any]"  [arg-type]

scikit-learn (https://github.com/scikit-learn/scikit-learn)
+ sklearn/conftest.py:347: error: Definition of "__class_getitem__" in base class "dict" is incompatible with definition in base class "spmatrix"  [misc]

discord.py (https://github.com/Rapptz/discord.py)
+ discord/ext/commands/converter.py:1143: error: Argument 1 of "__class_getitem__" is incompatible with supertype "builtins.list"; supertype defines the argument type as "TypeForm[Any]"  [override]
+ discord/ext/commands/converter.py:1143: note: This violates the Liskov substitution principle
+ discord/ext/commands/converter.py:1143: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides

cwltool (https://github.com/common-workflow-language/cwltool)
+ .../projects/_cwltool_venv/lib/python3.13/site-packages/galaxy/tool_util_models/parameter_validators.py:24: note: ... from here,
+ .../projects/_cwltool_venv/lib/python3.13/site-packages/galaxy/tool_util_models/parameters.py:57: note: ... from here,
+ .../projects/_cwltool_venv/lib/python3.13/site-packages/galaxy/tool_util_models/__init__.py:31: note: ... from here: