[WIP] Update docstrings of new tests according to RocketPy guidelines

[Copilot]

• Analyze PR ENH: Implementing 3-dof-simulation #745 to identify test files needing docstring updates
• Examine RocketPy docstring guidelines from existing test files
• Create tests/unit/motors/test_point_mass_motor.py with proper NumPy-style docstrings
• Create tests/unit/rocket/test_point_mass_rocket.py with proper NumPy-style docstrings
• Create tests/unit/simulation/test_flight_3dof.py with proper NumPy-style docstrings
• Run tests to verify the changes work correctly
• Run code review

Original prompt

#745 in the following PR please update all the docstrings of newly creates tests according to RocketPy guidelines.

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[aZira371]

Wrong branch selected by co pilot