ENH: implement `FrozenDict` with `frozendict` #639

Job	Run time
pytest / Determine job matrix	8s
style / Determine skipped pre-commit hooks	6s
doc / nb / Execute and build documentation	2m 6s
doc / linkcheck / Check external links	37s
style / Run local pre-commit hooks	34s
pytest / Run unit tests (3.10, ubuntu-24.04)	1m 9s
pytest / Run unit tests (3.11, ubuntu-24.04)	1m 3s
pytest / Run unit tests (3.9, ubuntu-24.04)	1m 2s
pytest / Run unit tests (3.12, ubuntu-24.04, qrules)	1m 53s
pytest / Run unit tests (3.9, macos-14)	1m 0s
style / Push changes	3s
doc / Upload to GitHub Pages	1s
	9m 42s

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