fix(python): drop typing.Type dependency for Python 3.6 target

[schani]

Bug

--lang python --python-version 3.6 generated code that imports and uses
typing.Type:

from typing import Any, TypeVar, Type, cast
...
def to_class(c: Type[T], x: Any) -> dict:

typing.Type was only added to the standard library in Python 3.5.3 / 3.6.1
— it does not exist in Python 3.6.0, the very first 3.6 release. This makes
quicktype's "3.6" output incompatible with that micro-version, even though
the user asked for 3.6 compatibility.

Root cause

The 3.6 preset in pythonOptions.features (packages/quicktype-core/src/language/Python/language.ts)
sets typeHints: true. With type hints enabled, JSONPythonRenderer
unconditionally emitted Type[T] (imported from typing) as the parameter
type hint for the c/t parameter of the generated to_class, to_enum,
and is_type helper functions — regardless of Python version.

Fix

Added a new typingType flag to PythonFeatures, set to false for the
3.5/3.6 presets and true for 3.7+ (where typing.Type has long been
available). JSONPythonRenderer now only emits the Type[T] annotation when
typingType is enabled; when it's disabled, the c/t parameter is left
without a type hint. All other type hints for Python 3.6 are unaffected, and
3.7+ output is unchanged.

Test coverage

Added test/unit/python-typing-type.test.ts, which generates code for both
Python 3.6 and 3.7 from a schema/JSON pair exercising to_class, to_enum,
and is_type, and asserts:

• Python 3.6 output never imports or references typing.Type.
• Python 3.7 output still imports and uses Type[T] as before (no
  regression for versions where typing.Type is safe to use).

The existing end-to-end Python fixture suite (test/languages.ts) already
parametrizes on python-version (3.5/3.6/3.7/3.9) via
quickTestRendererOptions, compiling generated code with mypy and
executing it — this continues to pass with the changed 3.6 output, verifying
the generated code stays syntactically valid and mypy-clean.

Verification performed locally

• npm run build — passes.
• Repro re-run: node dist/index.js --lang python --python-version 3.6 sample.json
  no longer imports/uses Type; --python-version 3.7 output is unchanged.
• npx vitest run test/unit/python-typing-type.test.ts — passes (2/2).
• QUICKTEST=true FIXTURE=python script/test — 61/61 tests pass, including
  the python-version: 3.5/3.6/3.7/3.9 combinations.
• biome check on changed files — clean.
• CI will run the full fixture matrix and unit suite.

Fixes #1728

🤖 Generated with Claude Code