Summary

• Add Python 3.15 typing additions and removals, including TypeForm, NoExtraItems, disjoint_base, TypeVarTuple attributes, and no_type_check_decorator removal.
• Update typing_extensions and _collections_abc exports for the Python 3.15 runtime surface.
• Remove corresponding 3.15 stubtest allowlist entries.

Relevant report entries

• Added typing.TypeForm and typing.disjoint_base; removed typing.no_type_check_decorator and typing.ByteString from typing.__all__ for 3.15; updated TypeVarTuple constructor surface (CPython PRs: Implement PEP 747: TypeForm cpython#145033, Implement PEP 800: typing.disjoint_base cpython#148639, Remove deprecated typing.no_type_check_decorator cpython#133601; source: https://github.com/python/cpython/blob/main/Lib/typing.py)
• Added typing.NoExtraItems and typing.TypeAliasType.__qualname__ for Python 3.15 (CPython source: https://github.com/python/cpython/blob/e81025e6d2e01e38c5a5b656af5739ac9df5ff55/Lib/typing.py, https://github.com/python/cpython/blob/e81025e6d2e01e38c5a5b656af5739ac9df5ff55/Objects/typevarobject.c)
• Removed collections.abc.ByteString from collections.abc.__all__ for 3.15 (source: https://github.com/python/cpython/blob/main/Lib/_collections_abc.py)