Implement PyErr::get_type_bound

[LilyFoote]

Implements more of the Bound api from #3684.

[codspeed-hq]

CodSpeed Performance Report

Merging #3819 will degrade performances by 16.95%

_{Comparing LilyFoote:pyerr-bound (c644893) with main (fa53d81)}

Summary

⚡ 2 improvements
❌ 2 regressions
✅ 75 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	LilyFoote:pyerr-bound	Change
⚡	list_via_extract	392.2 ns	336.7 ns	+16.5%
❌	not_a_list_via_downcast	216.7 ns	244.4 ns	-11.36%
⚡	f64_from_pyobject	461.1 ns	405.6 ns	+13.7%
❌	sequence_from_list	272.2 ns	327.8 ns	-16.95%

[davidhewitt]

Thank you for helping out with our great API migration!

There's a few thorny edge cases with reference counting that I've caught here. Comments below...

[davidhewitt]

Great, thanks!