clean up project root #1742

Job	Run time
windows (windows-latest, 3.12, tests/model)	19m 9s
ubuntu (ubuntu-latest, 3.10, tests/model)	11m 21s
windows (windows-latest, 3.12, tests/statespace/test_statespace.py)	16m 34s
ubuntu (ubuntu-latest, 3.10, tests/statespace/test_statespace.py)	9m 23s
windows (windows-latest, 3.12, tests/statespace/test_kalman_filter.py)	7m 59s
ubuntu (ubuntu-latest, 3.10, tests/statespace/test_kalman_filter.py)	3m 27s
windows (windows-latest, 3.12, tests/statespace --ignore tests/statespace/test_statespace.py --ig...	14m 27s
ubuntu (ubuntu-latest, 3.10, tests/statespace --ignore tests/statespace/test_statespace.py --igno...	8m 43s
windows (windows-latest, 3.12, tests/distributions)	14m 39s
ubuntu (ubuntu-latest, 3.10, tests/distributions)	8m 31s
windows (windows-latest, 3.12, tests --ignore tests/model --ignore tests/statespace --ignore test...	26m 9s
ubuntu (ubuntu-latest, 3.10, tests --ignore tests/model --ignore tests/statespace --ignore tests/...	15m 7s
all_tests	1s
	2h 35m 30s

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