Jacobian test for Exciter::SexsPti

[nkoukpaizan]

Description

This mainly adds a Jacobian test for Exciter::SexsPti

Proposed changes

• Added jacobian method to ExciterSexsPtiTests.hpp, testing the internal and bus Jacobians
• Added LoadZIP smoke tests to SystemSingleComponentTests.hpp, and todo items for Exciter::SexsPti and Stabilizer::Ieeest smoke tests.
• Minor comments and typo fixes

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.
• [N/A] 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

I'll work on abstracting away some of the Jacobian testing infrastructure to avoid having to duplicate the code.