Add support for Greybox model DOF counitng in degrees_of_freedom function #7083

Job	Run time
Check Spelling	8s
Check code formatting (Black)	34s
Compatibility tests	4m 22s
Build Sphinx docs	5m 15s
pytest (py3.9/linux)	18m 57s
Pylint	4m 17s
pytest (py3.9/win64)	29m 9s
pytest (py3.10/linux)	13m 54s
pytest (py3.10/win64)	32m 16s
pytest (py3.11/linux)	19m 26s
pytest (py3.11/win64)	39m 57s
pytest (py3.12/linux)	12m 27s
pytest (py3.12/win64)	27m 34s
Upload coverage report (Codecov) (linux)	10s
Upload coverage report (Codecov) (win64)	9s
	3h 28m 35s

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