Add support for cached_properties to slotted attrs classes. #737

Job	Run time
Build docs & run doctests	30s
Verify dev env (ubuntu-latest)	15s
Verify dev env (windows-latest)	49s
Check types using pyright	25s
Tests & Mypy on 3.7	39s
Tests & Mypy on 3.8	1m 6s
Tests & Mypy on 3.9	1m 8s
Tests & Mypy on 3.10	1m 19s
Tests & Mypy on 3.11	1m 21s
Tests & Mypy on 3.12	1m 23s
Tests & Mypy on pypy-3.8	55s
Tests & Mypy on pypy-3.9	54s
Tests & Mypy on pypy-3.10	54s
Combine & check coverage.	7s
required-checks-pass	6s
	11m 51s

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