Shorten the longest tests

[eric-wieser]

Today, these are:

198.76s call     clifford/test/test_algebra_initialisation.py::TestInitialisation::test_sparse_multiply[conformalize(Cl(3))]
40.55s call     clifford/test/test_algebra_initialisation.py::TestInitialisation::test_sparse_multiply[Cl(4)]
36.41s call     clifford/test/test_g3c_tools.py::TestRotorEstimation::test_estimate_rotor_optimisation[random_point_pair]
33.02s call     clifford/test/test_g3c_tools.py::TestModelMatching::test_fingerprint_match
23.04s call     clifford/test/test_g3c_tools.py::TestGeneralLogarithm::test_general_logarithm_conformal[random_point_pair]
20.31s call     clifford/test/test_g3c_tools.py::TestRotorEstimation::test_estimate_rotor_sequential[random_sphere]
17.68s call     clifford/test/test_g3c_tools.py::TestGeneralLogarithm::test_general_logarithm_conformal[random_line]
15.12s call     clifford/test/test_g3c_tools.py::TestGeneralLogarithm::test_general_logarithm_conformal[random_circle]
14.87s call     clifford/test/test_g3c_tools.py::TestGeneralLogarithm::test_general_logarithm_conformal[random_plane]
8.74s call     clifford/test/test_g3c_tools.py::TestG3CTools::test_enclosing_spheres
7.09s call     clifford/test/test_g3c_tools.py::TestModelMatching::test_iterative_model_match
6.53s call     clifford/test/test_tools.py::G3ToolsTests::test_rotation_matrix_conversions
6.20s call     clifford/test/test_g3c_tools.py::TestRotorEstimation::test_estimate_rotor_lines_average_then_opt
6.05s call     clifford/test/test_g3c_tools.py::TestFitObjects::test_fit_circle
5.60s call     clifford/test/test_g3c_tools.py::TestModelMatching::test_iterative_model_match_line_optimised
5.59s call     clifford/test/test_g3c_tools.py::TestRotorEstimation::test_estimate_rotor_optimisation[random_circle]

These tests alone eat up 7.426 minutes of our ~10 minute runtime