PyO3 0.23.4

This release contains a range of fixes on top of PyO3 0.23.3, primarily grouped into the following categories:

• Fixes for the new support for free-threaded Python 3.13
• Fixes to conversions between Python and chrono datetimes
• Fixes to various build configuration cases for Windows
• Fixes to edge cases in PyO3's macros leading to compile failures

Thank you to the following contributors for the improvements:

@alex
@bschoenmaeckers
@davidhewitt
@Icxolu
@kahojyun
@LilyFoote
@mejrs
@messense
@msimacek
@ngoldbaum
@Owen-CH-Leung
@Tpt