[fix] Make python unit tests be able to run successfully in the downstream package

[apaletta3]

Describe the bug
Due to a few missing imports and csv files that are currently used in the python unit tests, they don't pass when someone runs them from the python package itself.

python

E       NameError: name 'cesiumpy' is not defined

../viewer.py:70: NameError
============================================================== short test summary info ===============================================================
FAILED test_viewer.py::TestViewer::test_constructor_success - NameError: name 'cesiumpy' is not defined
ERROR estimator/test_orbit_determination_solver.py::TestOrbitDeterminationSolverAnalysis::test_constructor - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_orbit_determination_solver.py::TestOrbitDeterminationSolverAnalysis::test_properties - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_orbit_determination_solver.py::TestOrbitDeterminationSolver::test_estimate - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_orbit_determination_solver.py::TestOrbitDeterminationSolver::test_estimate_orbit - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_from_tle - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_from_state_b_star - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_from_state - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_invalid_initial_guess - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_invalid_state_only - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_no_observations - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_estimate_orbit - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR estimator/test_tle_solver.py::TestTLESolver::test_fit_with_different_frames - FileNotFoundError: [Errno 2] No such file or directory: '/app/test/OpenSpaceToolkit/Astrodynamics/Estimator/OrbitDeterminationSolverData/gnss_dat...
ERROR test_viewer.py::TestViewer::test_add_orbit_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_orbit_multiple_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_profile_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_target_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_target_with_label_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_line_success - NameError: name 'cesiumpy' is not defined
ERROR test_viewer.py::TestViewer::test_add_label_success - NameError: name 'cesiumpy' is not defined