Refine Elegant lattice converter

[Hespe]

Description

In the elegant lattice definition, there exist several aliases for already implemented cheetah Elements that prevent a sucessful import. This PR ensures that also the aliased elements can be imported without trouble.

Motivation and Context

• 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).

Note: We are using a maximum length of 88 characters per line.

[Hespe]

I have opted not to remove all traces of a potential charge element from the imported lattice, but instead to replace it with a Marker with the respective name. Maybe removing it completly would be nicer, but the Marker can always just be removed afterwards.

[jank324]

@Hespe can you make sure that the changes in this PR follow the new broadcasting semantics?

[Hespe]

There are a lot of square bracket in the Elegant converter that are probably no longer necessary with the broadcasting rules. They are, however, mostly in parts of the code that is not affected by this PR. Should we address that here, or leave it for another time? Doing it partially seems wrong.