Fix mypy errors in src/codegen/gscli/generate directory

[codegen-sh]

This PR fixes mypy errors in the src/codegen/gscli/generate directory by:

1. Adding proper type hints to functions and variables in commands.py:

   • Added return type annotations to functions
   • Added type annotations for variables like python_set, typescript_set, core_set, and mint_data
   • Added docstrings to functions that were missing them
   • Replaced exit(1) with sys.exit(1) for better type checking

2. Adding proper type hints to functions and variables in runner_imports.py:

   • Added return type annotations to functions
   • Added type annotations for variables like to_add and gs_public_imports
   • Used proper capitalized type names from the typing module (List, Set, Dict)

3. Adding proper type hints to functions and variables in utils.py (from a previous commit):

   • Added return type annotation to generate_builtins_file
   • Added type annotation for unique_imports

These changes improve type safety without changing the functionality of the code.

Note: This is a small PR focused only on fixing mypy errors in the generate directory as requested.