Stabilizer Docs + IEEEST Implementation

[lukelowry]

Description

Cleaned the Stabilizer folder in the PhasorDynamics to align it with the other models' folder structures. The documentation and implementation, or IEEEST, was also added.

This is one of the last essential models we need to faithfully model some of the larger cases. It's best to implement this before creating rigorous tests for big cases.

Proposed changes

• Make a general Stabilizer README
• Subfolder Stabilizer/PSS1A for the existing doc has been partially cleaned but not validated
• Subfolder Stabilizer/IEEEST with docs which should be the first stabilizer implemented.
• IEEEST Implementation
• The exciter and stabilizer can now be wired through the new external variable in IEEET1, vs.
• Lots of potentially unsafe parameters that are still valid model definitions, so I used a masking method that works with Enzyme. Not sure if it's optimal, but it works with a 240 bus case.

Checklist

• All tests pass. ( 44 - EnzymePowerElectronicsCheck is failing but that happens for me on development as well)
• 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.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

I have an uncommitted GENROU saturation fix and WECC 240 case that are pending this model!

The input signal delay is not implemented and is discussed in #369 . not a blocker

[abirchfield]

Looks great! Two issues with the documentation: the figure on the PSS1A model doesn't show, and the table on the IEEEST model doesn't render correctly on github.

[lukelowry]

@abirchfield @pelesh Updated! VSCode and GitHub rendering differently is strange.