Superimpose conversion

[roussel-ryan]

Description

Follow-on PR to #663 that implements proper conversion of superimposed elements in bmad to Superimposed elements in cheetah and conversion of those elements to json. The superimpose element will contain the reference element name (ie. QE01) while prepending _ to the reference element when assigning it to the base_element in the Superimposed cheetah object. When flattening, the base element halves will be given _1 and _2 at the end (ie. QE01_1,QE01_2) to be consistent with bmad convention.

Motivation and Context

This change is needed to properly import LCLS bmad lattices.

• I have raised an issue to propose this change (required for new features and bug fixes)

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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