Cleanup Python code for generators (#33)

* Clean up layer and common generator code
* Add these to the Actions runner Python style and typing checks

Author: solidpixel

.github/workflows/build_test.yaml

@@ -30,10 +30,12 @@ jobs:
       - name: Check code style
         run: |
           python3 -m pycodestyle ./lglpy
+          python3 -m pycodestyle ./generator
 
       - name: Check typing
         run: |
           python3 -m mypy ./lglpy
+          python3 -m mypy ./generator
 
   build-ubuntu-x64-clang:
     name: Ubuntu x64 Clang