PhasorDynamics simulations with sparse Jacobians

[nkoukpaizan]

Description

This adds the ability to run PhasorDynamics examples with sparse Jacobian. The component Jacobians are obtained with Enzyme and assembled into the system Jacobian.

cc @lukelowry @abirchfield

Proposed changes

• Added missing Jacobian block terms such as $\partial f/\partial y'$, $\partial h/\partial y$ and $\partial f/\partial w_b$
• Added verification in the unit tests for the $\partial f/\partial y'$ terms
• Multiple bug fixes

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.
• 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

This is still using COO_Matrix. I suggest we merge #307 and re-use Jacobian assembly.

Comparison plots between current (sparse Jacobians) and reference (dense Jacobians computed by IDA with finite differences)

ThreeBus_Basic

ThreeBus_Classical

TenGenGenrou

TenGenGenClassical

[pelesh]

Great job! All tests pass and the PR fixes quite a few minor issues along the way. I left a few nitpicking comments mainly requesting better documentation within the code.

[PhilipFackler]

Looks good!