Add a Sphinx extension to document cached properties of slots classes #2005

Job	Run time
Check types using supported type checkers	19s
Build & verify package	21s
Verify dev env	12s
Run doctests & render changelog	20s
Tests & Mypy on 3.11	1m 7s
Tests & Mypy on 3.12	1m 9s
Tests & Mypy on 3.13	1m 4s
Tests & Mypy on 3.9	42s
Tests & Mypy on 3.14	1m 22s
Tests on pypy-3.10	21s
Tests & Mypy on 3.10	1m 9s
Combine & check coverage	15s
required-checks-pass	3s
	8m 24s

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