tests/test_nanshe_learner.py: Added code to generate 3D test data for regression tests.
tests/test_nanshe_learner.py: Added a test for nanshe.nanshe_learner.main using 3D data.
tests/test_nanshe_learner.py: Modified the test for nanshe.nanshe_learner.main using 3D data to work on a smaller dataset.
tests/test_nanshe_learner.py: Added a test for nanshe.nanshe_learner.generate_neurons_io_handler using 3D data.
tests/test_nanshe_learner.py: Added a test for nanshe.nanshe_learner.generate_neurons_a_block using 3D data.