Expand documentation for phasor dynamics model structure

Summary

Expand documentation in the PhasorDynamics README file and comments in source code in Component, GridElement, and Bus* classes.

Rationale

Doxygen style comments would help create documentation automatically and some description of the model code architecture in the README file would be helpful for component-model developers. Ideally, we want power systems experts to have clear understanding how to add a new component model without diving deep in GridKit code.

Description

• In GridKit/Model/PhasorDynamics/README.md file add an overview of model classes architecture and some general instructions for component model developers.
• Add new and expand existing comments following Doxygen markup for following classes"
  • GridElement
  • BusBase
  • BusBaseImpl
  • Component

Additional information

No response