Mapping returns PyList for keys, values, and items

[KLMatlock]

From the PyMappingProxy PR.

Since Python 3.7 PyMapping_Keys, PyMapping_Values, and PyMapping_Items always returns a list instead of a sequence. This PR updates the corresponding return types in PyMapping.

[davidhewitt]

Thanks, I guess this needs rebasing on main now that #4644 was merged :)

[codspeed-hq]

CodSpeed Performance Report

Merging #4661 will improve performances by 16.35%

_{Comparing KLMatlock:mapping-returns-pylist (2119dcc) with main (2d3bdc0)}

Summary

⚡ 5 improvements
✅ 78 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	KLMatlock:mapping-returns-pylist	Change
⚡	test_empty_class_init_py	15.3 µs	13.8 µs	+10.86%
⚡	test_args_kwargs_py	21.1 µs	18.4 µs	+14.81%
⚡	test_args_kwargs_rs	15.8 µs	13.6 µs	+16.35%
⚡	test_simple_kwargs_py	22.3 µs	20 µs	+11.66%
⚡	test_simple_kwargs_rs	21.6 µs	18.8 µs	+14.58%

[davidhewitt]

Thanks 👍