PyO3 0.29.1

This patch is a stack of fixes for PyO3 0.29. Particular themes include:

• Fixes addressing build failures with newer interpreters such as GraalPy 3.13 and CPython 3.15
• Fixes resolving potential memory leaks inside #[pyclass] implementation internals
• Fixes to the new experimental-inspect type stub machinery

For a full list of the fixes in these above themes and more, please consult the CHANGELOG.

Thank you to the following contributors for the improvements:

@alex
@bschoenmaeckers
@chirizxc
@davidhewitt
@dependabot[bot]
@exg
@ImFeH2
@IvanIsCoding
@jonasdedden
@MatthieuDartiailh
@msimacek
@ngoldbaum
@Person-93
@ratazzi
@rewitt94
@scott-griffiths
@ShiroKSH
@tobni
@Tpt
@WaterWhisperer