convert python scripts to notebooks

[shimwell]

• task_04_make_sources/6_unstructured_mesh_spatial_source.py
• task_04_make_sources/7_strucutured_mesh_source.py
• task_05_CSG_cell_tally_TBR/example_tritium_production_study_with_openmc_lib.py
• task_09_CSG_instantaneous_dose_tallies/3_cell_dose_from_neutron.py
• task_09_CSG_instantaneous_dose_tallies/4_cell_dose_from_photon.py
• task_09_CSG_instantaneous_dose_tallies/5_mesh_dose_from_neutrons.py
• task_09_CSG_instantaneous_dose_tallies/compare_dose_simulation_with_back_of_envelope.py
• task_10_activation_transmutation_depletion/0_simple_transmutation_reaction_rate_simulation.py
• task_11_CSG_shut_down_dose_tallies/1_cell_based_shut_down_dose_rate_example.py
• task_11_CSG_shut_down_dose_tallies/2_faster_mulitiple_puse_shut_down_dose_rate_example.py
• task_12_detectors_examples/1_time_filter_tally.py
• task_12_detectors_examples/2_time_filter_tally_with_reflective_sphere.py
• task_12_detectors_examples/3_time_and_energy_filter_tally.py