implement tcav splitting

[roussel-ryan]

Implement TCAV num_steps and splitting

Description

Correctly implements TCAV num_steps specification and element splitting in limited cases (num_steps of original element must be odd and greater than 1).

Motivation and Context

This is needed for effective tracking in lcls lattices since TCAV elements contain steering elements that are modeled by splitting the TCAV element into 2 parts. This correctly splits the elements by breaking the tracking steps up properly while also correctly scaling the TCAV voltage to maintain correct tracking. This improvement is in conjunction with #591

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code and checked that formatting passes (required).
• I have have fixed all issues found by flake8 (required).
• I have ensured that all pytest tests pass (required).
• I have run pytest on a machine with a CUDA GPU and made sure all tests pass (required).
• I have checked that the documentation builds (required).

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