Remove `COO_Matrix` from PowerElectronics module

[pelesh]

Summary

Remove COO_Matrix from components and system model in PowerElectronics module. Use raw data arrays to store Jacobian matrix elements for individual component models.

Rationale

With improved Jacobian assembly in PowerElectronics module in #339, the COO_Matrix object has become obsolete. It remains only in component models where it is used to store local Jacobian stamps. By replacing COO_Matrix with raw data arrays in component models, we simplify component implementation, make code more readable and eliminate overhead of redundant objects.

Description

• Replace COO_Matrix object with raw data arrays for matrix row indices, column indices and values.
• Modify PowerElectronicsModel::evaluateJacobian() method accordingly.
• Remove COO_Matrix type from all PowerElectronics classes (accessed through Evaluator<ScalarT, IdxT>::MatrixT type).
• Update verification tests accordingly.

Additional information

No response

[alexander-novo]

Right now, the Evaluator class has a getJacobian() function which returns a COO_Matrix&. When getting rid of the COO_Matrix class, do you think this should be replaced with

1. The same function, returning a CooMatrix&, which was introduced in Refactor Jacobian assembly #339
2. The same function, returning a thin struct that just contains pointers to the data arrays as well as nnz
3. A variety of functions e.g. getJacobianRows(), getJacobianCols(), getJacobianNnz(), etc.

[pelesh]

I would definitely avoid option 1., it is an overkill.

[pelesh]

Note that in PowerElectronicsModel::allocate you only need arrays with components' Jacobians row and column indices.

In PowerElectronicsModel::evaluateJacobian you only need components' Jacobians values.

There is already method to return NNZ for each component.

[alexander-novo]

Okay I'll go with the third option, then, keeping the nnz() function.