Add Py::drop_ref method

[juntyr]

Adds the Py::drop_ref method to explicitly drop a Py and immediately decrease the Python reference count if the GIL is already held.

Fixes #3870

[davidhewitt]

Thanks! I have a couple of quick thoughts...

[codspeed-hq]

CodSpeed Performance Report

Merging #3871 will not alter performance

_{Comparing juntyr:py-drop-ref (5f35069) with main (0bb9cab)}

Summary

✅ 67 untouched benchmarks

⁉️ 12 dropped benchmarks

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

Benchmarks breakdown

	Benchmark	main	juntyr:py-drop-ref	Change
⁉️	mapping_from_dict	327.8 ns	N/A	N/A
⁉️	extract_float_downcast_success	453.3 ns	N/A	N/A
⁉️	extract_float_extract_success	417.2 ns	N/A	N/A
⁉️	extract_int_downcast_fail	300.6 ns	N/A	N/A
⁉️	extract_int_downcast_success	642.2 ns	N/A	N/A
⁉️	extract_int_extract_success	606.1 ns	N/A	N/A
⁉️	f64_from_pyobject	405.6 ns	N/A	N/A
⁉️	list_via_downcast	157.2 ns	N/A	N/A
⁉️	list_via_extract	336.7 ns	N/A	N/A
⁉️	not_a_list_via_downcast	244.4 ns	N/A	N/A
⁉️	sequence_from_list	355.6 ns	N/A	N/A
⁉️	sequence_from_tuple	267.2 ns	N/A	N/A

[davidhewitt]

Overall I think the implementation and documentation for this is great! As a final step, could you please add a test? 🙏

[davidhewitt]

Looks good to me, thanks very much! 🚀