Add a Sphinx extension to document cached properties of slots classes #2008

Job	Run time
Build & verify package	22s
Verify dev env	55s
Check types using supported type checkers	55s
Tests & Mypy on 3.13	12s
Tests on pypy-3.10	17s
Tests & Mypy on 3.10	15s
Run doctests & render changelog	9s
Tests & Mypy on 3.11	13s
Tests & Mypy on 3.9	16s
Tests & Mypy on 3.12	10s
Tests & Mypy on 3.14	12s
Combine & check coverage	-1s
required-checks-pass	3s
	3m 58s

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