PyO3 0.19.1

This release fixes a memory leak caused by a reference counting error which affected PySet::new, PyFrozenSet::new and conversions from Rust set types to Python's set.

There are several other notable quality-of-life changes in this release:

• Support for PyPy 3.10.
• Support for hashbrown 0.14 and indexmap 2.0.
• Conversions for std::net::IpAddr have been added.
• The num-bigint feature is now supported with the abi3 feature.
• The num-complex feature with abi3 feature enabled will now correctly use __complex__ implementations (it always has without abi3 enabled).
• #[new] methods can now return Py<Self> to return an existing object (e.g. for singleton classes).

There are also a handful of other additions and bugfixes included in this release.

Thank you to the following users for the improvements:

@adamreichold
@adriangb
@alex
@CallMeMSL
@davidhewitt
@ijl
@jakelishman
@lucatrv
@mejrs
@mhils
@youknowone