[DEV]: v2.9.0 - Python3.14 compat & new features

[MatrixEditor]

What is planned for this pull request:

• Add Python 3.14-compatible conditional metadata support.
• Add generic TypeVar templates
• Add inline anonymous unions with named raw field support. (deferred)
• Add padding wrappers,
• fix C/Python interop
• Add more tests and (finally) some benchmarks

Details

• Python generic templates based on normal typing.TypeVar and Generic classes. Templates now support direct Template[uint8] specialization, partial specialization, specialization caching, and runtime __origin__ / __args__ metadata; e.g.

  T = TypeVar("T")

  @template
  class Box(Generic[T]):
      value: T

  ByteBox = Box[uint8_t] # type checkers will love this