Update and Refactor `find_MAP` and `fit_laplace` #1919

Job	Run time
windows (windows-latest, 3.12, tests/model)	13m 32s
windows (windows-latest, 3.12, tests/statespace --ignore tests/statespace/core/test_statespace.py...	11m 53s
windows (windows-latest, 3.12, tests/statespace/core/test_statespace.py)	9m 45s
windows (windows-latest, 3.12, tests/distributions)	10m 59s
windows (windows-latest, 3.12, tests/statespace/filters/test_kalman_filter.py)	4m 47s
ubuntu (ubuntu-latest, 3.11, tests/statespace/filters/test_kalman_filter.py)	2m 31s
windows (windows-latest, 3.12, tests --ignore tests/model --ignore tests/statespace --ignore test...	17m 11s
ubuntu (ubuntu-latest, 3.11, tests/statespace/core/test_statespace.py)	6m 16s
ubuntu (ubuntu-latest, 3.11, tests/statespace --ignore tests/statespace/core/test_statespace.py -...	7m 14s
ubuntu (ubuntu-latest, 3.11, tests --ignore tests/model --ignore tests/statespace --ignore tests/...	9m 11s
ubuntu (ubuntu-latest, 3.11, tests/model)	8m 49s
ubuntu (ubuntu-latest, 3.11, tests/distributions)	6m 21s
all_tests	3s
	1h 48m 32s

Provide feedback