Make basic INLA interface and simple marginalisation routine #2192

Job	Run time
windows (windows-latest, 3.12, tests/statespace/filters/test_kalman_filter.py)	4m 26s
windows (windows-latest, 3.12, tests/statespace --ignore tests/statespace/core/test_statespace.py...	19m 40s
windows (windows-latest, 3.12, tests/model)	18m 47s
windows (windows-latest, 3.12, tests/statespace/core/test_statespace.py)	11m 49s
windows (windows-latest, 3.12, tests --ignore tests/model --ignore tests/statespace --ignore test...	19m 33s
ubuntu (ubuntu-latest, 3.11, tests/statespace/filters/test_kalman_filter.py)	3m 12s
windows (windows-latest, 3.12, tests/distributions)	13m 12s
ubuntu (ubuntu-latest, 3.11, tests/model)	9m 35s
ubuntu (ubuntu-latest, 3.11, tests/statespace --ignore tests/statespace/core/test_statespace.py -...	12m 22s
ubuntu (ubuntu-latest, 3.11, tests/statespace/core/test_statespace.py)	9m 35s
ubuntu (ubuntu-latest, 3.11, tests/distributions)	6m 53s
ubuntu (ubuntu-latest, 3.11, tests --ignore tests/model --ignore tests/statespace --ignore tests/...	12m 2s
all_tests	3s
	2h 21m 9s

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