Replace as_ref(py) with Bound APIs

[LilyFoote]

Following the merge of #3705 we can tidy these up.

[codspeed-hq]

CodSpeed Performance Report

Merging #3863 will degrade performances by 16.65%

_{Comparing LilyFoote:more-as-ref-replacements (0a4c9b5) with main (0bb9cab)}

Summary

⚡ 3 improvements
❌ 3 regressions
✅ 73 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	LilyFoote:more-as-ref-replacements	Change
⚡	mapping_from_dict	327.8 ns	272.2 ns	+20.41%
❌	extract_float_downcast_success	453.3 ns	536.7 ns	-15.53%
❌	extract_float_extract_success	417.2 ns	500.6 ns	-16.65%
❌	list_via_downcast	157.2 ns	185 ns	-15.02%
⚡	not_a_list_via_downcast	244.4 ns	216.7 ns	+12.82%
⚡	sequence_from_list	355.6 ns	272.2 ns	+30.61%

[davidhewitt]

Looks great, thanks. Added a new suggestion for the doc comment. (Maybe just drop that from this PR if you like my alternative proposal?) Otherwise good to merge!