State Sync + Simulation Performance

[lukelowry]

Description

In my feature branch, where I have larger models with more signals, I was running into some strange state synchronization issues between the machine, exciter, and bus. I noticed that Ida.cppand SystemModel.hpp seem to pass state in a different order, fixing the inter-model issues I had. Ida stopped failing during fault events in a 240-Bus case I am constructing, and it reduced the solve time by ~3x across all examples.

I'm not sure why this has such a big impact on performance, or whether it's related to my build configuration. Worth looking at because GK now simulates faster than PowerWorld for my machine on this branch, but not on the develop branch.

Example of change

Before

  model->updateTime(tres, 0.0);
  copyVec(yy, model->y());
  copyVec(yp, model->yp());

After (i.e., share state before invoking so it's not stale)

  copyVec(yy, model->y());
  copyVec(yp, model->yp());
  model->updateTime(tres, 0.0);

Closes #(issue)

Mentions @(user)

Proposed changes

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Checklist

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• 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.

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