Represent statespace metadata with dataclasses #2295

Job	Run time
windows (windows-latest, 3.12, tests/model)	9m 10s
ubuntu (ubuntu-latest, 3.11, tests/model)	5m 8s
windows (windows-latest, 3.12, tests/statespace/core/test_statespace.py)	12m 54s
ubuntu (ubuntu-latest, 3.11, tests --ignore tests/model --ignore tests/statespace --ignore tests/...	5m 39s
windows (windows-latest, 3.12, tests --ignore tests/model --ignore tests/statespace --ignore test...	18m 46s
ubuntu (ubuntu-latest, 3.11, tests/statespace --ignore tests/statespace/core/test_statespace.py -...	8m 43s
ubuntu (ubuntu-latest, 3.11, tests/distributions)	3m 5s
ubuntu (ubuntu-latest, 3.11, tests/statespace/core/test_statespace.py)	8m 0s
windows (windows-latest, 3.12, tests/statespace/filters/test_kalman_filter.py)	5m 2s
windows (windows-latest, 3.12, tests/distributions)	6m 10s
windows (windows-latest, 3.12, tests/statespace --ignore tests/statespace/core/test_statespace.py...	15m 46s
ubuntu (ubuntu-latest, 3.11, tests/statespace/filters/test_kalman_filter.py)	2m 35s
all_tests	3s
	1h 41m 1s

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