pow-migration: Update comments and clean up code

[jsdanielh]

• Update comments and clean up code
  • Update comments and documentation.
  • Clean up code by using better code patterns and remove unnecessary indentation.
• Re-organize code for simplicity:
  • Removed duplicated types.
  • Moved all types to a single place.
  • Remove unnecessary directory nesting.

Pull request checklist

• [X] All tests pass. The project builds and runs.
• [X] I have resolved any merge conflicts.
• [X] I have resolved all clippy and rustfmt warnings.