Represent statespace metadata with dataclasses #2294

Job	Run time
ubuntu (ubuntu-latest, 3.11, tests/statespace/filters/test_kalman_filter.py)	56s
windows (windows-latest, 3.12, tests/statespace/filters/test_kalman_filter.py)	47s
ubuntu (ubuntu-latest, 3.11, tests/statespace --ignore tests/statespace/core/test_statespace.py -...	56s
ubuntu (ubuntu-latest, 3.11, tests --ignore tests/model --ignore tests/statespace --ignore tests/...	58s
ubuntu (ubuntu-latest, 3.11, tests/distributions)	58s
ubuntu (ubuntu-latest, 3.11, tests/statespace/core/test_statespace.py)	58s
windows (windows-latest, 3.12, tests/statespace --ignore tests/statespace/core/test_statespace.py...	51s
ubuntu (ubuntu-latest, 3.11, tests/model)	58s
windows (windows-latest, 3.12, tests --ignore tests/model --ignore tests/statespace --ignore test...	52s
windows (windows-latest, 3.12, tests/statespace/core/test_statespace.py)	50s
windows (windows-latest, 3.12, tests/model)	52s
windows (windows-latest, 3.12, tests/distributions)	51s
all_tests	3s
	10m 50s

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