Make #wrap_pyfunction return a Bound value

[snuderl]

Part of Part of https://github.com/PyO3/pyo3/issues/3684

This is a tehnically a breaking change. The diff is pretty simple though which hopefully means not many users would be impacted in practice. Thoughts?

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #3808 will degrade performances by 12.82%

_{Comparing snuderl:wrap_pyfunction-bound (0e43071) with main (030a618)}

Summary

⚡ 5 improvements ❌ 1 regressions ✅ 73 untouched benchmarks

:warning: Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	snuderl:wrap_pyfunction-bound	Change
⚡	not_a_list_via_downcast	242.8 ns	215 ns	+12.92%
⚡	mapping_from_dict	327.8 ns	272.2 ns	+20.41%
❌	f64_from_pyobject	377.8 ns	433.3 ns	-12.82%
⚡	sequence_from_list	355.6 ns	300 ns	+18.52%
⚡	extract_str_downcast_fail	266.1 ns	238.3 ns	+11.66%
⚡	extract_int_downcast_fail	266.1 ns	238.3 ns	+11.66%

[Icxolu]

There might be an option to avoid the breakage for PyModule::add_function. I think we could return a "private" wrapper type around Bound<PyCFunction> in _wrap_pyfunction, which implements From conversions for both Bound and gil-ref, and then perform the Into conversion inside the wrap_pyfunction macro.

[davidhewitt]

I think we resolved this with new tricks in #3897. Thanks @snuderl for kicking this off and sorry we ended up going in a different direction...