docs: migrate documentation site from Sphinx to MkDocs #535

Job	Run time
build / lint-rust	1m 53s
build / generate-license	2m 24s
build / lint-python	9s
build / lint-toml	5s
build / check-crates-patch	0s
build / Linux x86_64 (abi3)	19m 37s
build / Linux x86_64 (3.14t)	14m 34s
build / Linux arm64 (abi3)	11m 55s
build / Linux arm64 (3.14t)	12m 17s
build / Linux arm64 (3.13t)	11m 51s
build / macOS arm64 (3.13t)	10m 7s
build / Windows x86_64 (3.13t)	21m 29s
build / macOS arm64 (3.14t)	9m 37s
build / Windows x86_64 (3.14t)	12m 54s
build / Linux x86_64 (3.13t)	14m 1s
build / macOS arm64 (abi3)	14m 5s
build / Windows x86_64 (abi3)	12m 51s
build / Source distribution	0s
build / macOS x86_64 (${{ matrix.python-tag }})	0s
build / Build docs	34s
build / Merge build artifacts	-1s
test	-1s
	2h 50m 21s

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