Implement tagDifferentiable in PowerElectronics models

[alexander-novo]

Description

Implemented tagDifferentiable() in PowerElectronics models, so that they can be used for scaling testing of Rosenbrock.

Proposed changes

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.

Further comments