Classical Generator Updates and Completion

[lukelowry]

Description

Update GenClassical to have recent conventions and implementation. Adds functionality to the signal ports, so governors, exciters, and stabilizers now connect to it the same way they connect to other machines.

Proposed changes

• Add GenClassicalInternalVariables/GenClassicalExternalVariables and ComponentSignals with pmech and efd inputs and a speed output.
• Replace the default and positional constructors with the data constructor; remove setPmech/setEp, bus_id_, and the dead exciter_signal/governor_signal inputs.
• Add the DfDws block to the Enzyme Jacobian and link the signal libraries.
• Rewrite the README to the current notation and section standard.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• Changelog changes are N/A; this is a focused cleanup of an existing model implementation.

Further comments

Could not be connected to controllers before this PR because we started governor and exciter integration with Genrou

[lukelowry]

@nkoukpaizan As long as the CI passes then I agree!