Create phasor dynamics model data structures

[pelesh]

Description

@abirchfield @lukelowry @alexander-novo @reid-g @abdourahmanbarry

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.

Further comments

[superwhiskers]

i don't think this is related to any change made in this pull request, but there's a segfault in the example AdjointSens in the destructor AnalysisManager::Sundials::Ida::~Ida caused by Ida::deleteAdjoint() calling IDAAdjFree(solver_) and then Ida::deleteSimulation() calling IDAFree(&solver_) which calls IDAAdjFree(...) as well. from what i can tell, the best way to solve this would be to remove the call to Ida::deleteAdjoint() in the destructor, but i could be wrong about this.

[pelesh]

i don't think this is related to any change made in this pull request, but there's a segfault in the example AdjointSens in the destructor AnalysisManager::Sundials::Ida::~Ida caused by Ida::deleteAdjoint() calling IDAAdjFree(solver_) and then Ida::deleteSimulation() calling IDAFree(&solver_) which calls IDAAdjFree(...) as well. from what i can tell, the best way to solve this would be to remove the call to Ida::deleteAdjoint() in the destructor, but i could be wrong about this.

This issue was supposed to be fixed in SUNDIAL PR 704. For now, we need to use SUNDIALS from develop branch.

[pelesh]

Closing this in favor of #116.