Implement frame drawing (#168)

* Coloured boxes are used by default when the diagram has frames but can be turned off using `color_boxes=False`
* Fixed a bug in the `TikzBackend` that messes up the connectivity in the output drawing

Author: neiljdo

.github/workflows/build_test.yml

@@ -73,7 +73,7 @@ jobs:
     - name: Test with pytest
       run: >
         coverage run --source=${{ env.SRC_DIR }}
-        --module pytest ${{ env.TEST_DIR }}
+        --module pytest -vvv ${{ env.TEST_DIR }}
         --durations=50
         --ignore=${{ env.TEST_DIR }}/text2diagram/test_depccg_parser.py
         --ignore=${{ env.TEST_DIR }}/training/test_torchquantum_model.py