4.12.0rc1

This release focuses on compatibility with the upcoming release of
Python 3.13. Most changes are related to the implementation of type
parameter defaults (PEP 696).

Thanks to all of the people who contributed patches, especially Alex
Waygood, who did most of the work adapting typing-extensions to the
CPython PEP 696 implementation.

Full changelog:

• Improve the implementation of type parameter defaults (PEP 696)
  • Backport the typing.NoDefault sentinel object from Python 3.13.
    TypeVars, ParamSpecs and TypeVarTuples without default values now have
    their __default__ attribute set to this sentinel value.
  • TypeVars, ParamSpecs and TypeVarTuples now have a has_default()
    method, matching typing.TypeVar, typing.ParamSpec and
    typing.TypeVarTuple on Python 3.13+.
  • TypeVars, ParamSpecs and TypeVarTuples with default=None passed to
    their constructors now have their __default__ attribute set to None
    at runtime rather than types.NoneType.
  • Fix most tests for TypeVar, ParamSpec and TypeVarTuple on Python
    3.13.0b1 and newer.
  • Backport CPython PR #118774,
    allowing type parameters without default values to follow those with
    default values in some type parameter lists. Patch by Alex Waygood,
    backporting a CPython PR by Jelle Zijlstra.
  • It is now disallowed to use a TypeVar with a default value after a
    TypeVarTuple in a type parameter list. This matches the CPython
    implementation of PEP 696 on Python 3.13+.
  • Fix bug in PEP-696 implementation where a default value for a ParamSpec
    would be cast to a tuple if a list was provided.
    Patch by Alex Waygood.
• Fix Protocol tests on Python 3.13.0a6 and newer. 3.13.0a6 adds a new
  __static_attributes__ attribute to all classes in Python,
  which broke some assumptions made by the implementation of
  typing_extensions.Protocol. Similarly, 3.13.0b1 adds the new
  __firstlineno__ attribute to all classes.
• Fix AttributeError when using typing_extensions.runtime_checkable
  in combination with typing.Protocol on Python 3.12.2 or newer.
  Patch by Alex Waygood.
• At runtime, assert_never now includes the repr of the argument
  in the AssertionError. Patch by Hashem, backporting of the original
  fix python/cpython#91720 by Jelle Zijlstra.
• The second and third parameters of typing_extensions.Generator,
  and the second parameter of typing_extensions.AsyncGenerator,
  now default to None. This matches the behaviour of typing.Generator
  and typing.AsyncGenerator on Python 3.13+.
• typing_extensions.ContextManager and
  typing_extensions.AsyncContextManager now have an optional second
  parameter, which defaults to Optional[bool]. The new parameter
  signifies the return type of the __(a)exit__ method, matching
  typing.ContextManager and typing.AsyncContextManager on Python
  3.13+.
• Backport types.CapsuleType from Python 3.13.
• Releases are now made using Trusted Publishers
  improving the security of the release process. Patch by Jelle Zijlstra.