pyclass methods for Bound

[davidhewitt]

Split from #3606

This PR adds new methods to Bound<T: PyClass> to access the inner T via PyRef<T>, PyRefMut<T> and &T.

These methods are identical to the ones on Py<T>.

Given that we want to remove the GIL Ref &PyCell<T>, I think it is correct to add these methods to Bound<T> as a replacement.

[adamreichold]

Is there something we'd want to conditionally deprecate here? I don't think the corresponding methods on PyCell are reasonable, but some way to produce a &PyCell? But I guess this will usually happen behind the scenes a function/method arguments?

[davidhewitt]

Yes I think that any associated deprecation would be the same one that deprecates getting GIL Refs in general, if we can find a nice pattern for that. Probably by deprecating .as_gil_ref() and .into_gil_ref() methods plus finding a mechanism to deprecate the function arguments in macro code.

[davidhewitt]

(Or maybe we deprecate PyCell completely, #3792 (comment). Probably too much to do just in this PR, however.)

[davidhewitt]

Thanks for the approval! I'll push some coverage and merge 👍

[codspeed-hq]

CodSpeed Performance Report

Merging #3792 will improve performances by 20.41%

_{Comparing davidhewitt:bound-pyclass-2 (42843de) with main (7938d4c)}

🎉 Hooray! codspeed-rust just leveled up to 2.3.3!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

⚡ 3 improvements
✅ 76 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	davidhewitt:bound-pyclass-2	Change
⚡	not_a_list_via_downcast	242.8 ns	215 ns	+12.92%
⚡	mapping_from_dict	327.8 ns	272.2 ns	+20.41%
⚡	sequence_from_list	355.6 ns	300 ns	+18.52%