[rejected AI] Path is generic on path_type

[dhimasardinata]

Fixes #3822.

MRE from the issue now passes on mypy, pyright, and ty:

import pathlib
from typing_extensions import assert_type
import click

my_type = click.Path(file_okay=False, path_type=pathlib.Path)
path = click.prompt("Enter a name", type=my_type)
assert_type(path, pathlib.Path)

What changed (runtime unchanged, typing only):

• Path is now ParamType[_PathValueT_co], Generic[_PathValueT_co] with a PEP 696 default (str | bytes | os.PathLike[str]), matching the existing ParamType second-param pattern for py3.10 compat.
• __init__ overloads infer Path[T] from path_type: type[T]; bare Path() keeps the default union.
• convert / coerce_path_result return the generic value type; self.type annotated as builtins.type[...] | None (avoids shadowing the type attribute).
• Added tests/typing/typing_path.py assert_type coverage and CHANGES entry.

Verified:

• mypy clean (29 files, strict)
• pyright --ignoreexternal --verifytypes click 100% + 0 errors on new typing test and issue MRE
• ruff check + ruff format --check clean
• pytest tests/test_types.py 45 passed; manual runtime smoke (str/bytes/pathlib converts, Path[pathlib.Path] alias) unchanged.

[davidism]

https://palletsprojects.com/contributing/llm-ai