[aiofiles] Fix NamedTemporaryFile name type

[nightcityblade]

Fixes #13551

What problem this solves

aiofiles.tempfile.NamedTemporaryFile() currently exposes name as the broad FileDescriptorOrPath type, unlike the named temporary-file API it wraps.

Why this change

The general async file wrappers must retain their broad name type because aiofiles.open() accepts file descriptors and path-like values. This adds private named-temporary-file wrapper types that narrow only NamedTemporaryFile() results to str.

User impact

Type checkers now accept string-specific operations on file.name inside both binary and text NamedTemporaryFile() context managers.

Evidence

• Added regression assertions for default binary and text modes.
• source .venv/bin/activate && python tests/runtests.py stubs/aiofiles --run-stubtest
  • pre-commit, structure, Pyright, ty, pyrefly, mypy, stubtest, and both regression suites passed.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉