Minor performance improvements to PowerElectronics residual evaluation

[alexander-novo]

Description

Changed connection_nodes_ to an array to prevent tree searches in hot loops.

There are some virtual functions implemented by CircuitComponent which aren't marked final or const and are called in a couple of hot loops inside evaluateResidual(). The optimizer can't inline these functions or perform LICM, so these functions end up being called billions of times during the simulation, which contributes a few percents to the overall runtime of the simulation.

I've gone through and marked many of these functions as final and added const variants. These functions could probably be marked as const in Evaluator, but I didn't want to change something that would affect the phasor dynamics module without a thumbs up.

I've also manually performed LICM in the hot loops in evaluateResidual() because I don't want to depend on the optimizer getting this right - this could very easily regress in the future.

Closes #324

Proposed changes

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

[pelesh]

Great work! Please fix changeling conflict before merging.