Handle energy spread units in source generation

[Atraxus]

Type of Change

• Bug fix (non breaking change, fixing an issue)
• New feature
• Breaking change (fix or feature that causes existing functionality to not work as expected)
• Documentation / Wiki update

Description

Correct parsing of the energy spread unit. It was not implemented before but the behavior for users is very confusing so I'll classify this as a bugfix.

Fixed #470

Optional notes for reviewer:

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✅ Pre-Merge Checklist

Important

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• Code follows the project's coding standards
• Unit tests for new functionality are added and pass
• All existing tests pass
• Resolved TODO Comments (prefer new issues instead)
• Documentation, if applicable, including:
  • Doxygen comments for any new rayx-core API functions
  • Helpful inline comments where needed for clarity
  • Wiki pages, e.g. updated build instructions, new Element etc.
• Commits:
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  • Squash and rebase onto master if individual commits don’t add value
  • Ensure linear commit history (required by master)

[MMXLVIII]

minor changes, can merge afterwards