Preserve trailing underscores in type name normalization

[Copilot]

XSD types differing only by trailing underscores (e.g., Base_ and Base) caused TypeAlreadyDefined errors when both referenced the same group, as the name normalization collapsed them to identical identifiers.

Changes

• Modified Naming::unify() in traits/naming.rs: Strip trailing underscores before PascalCase conversion, then re-append them to preserve distinctness
• Added unit tests: Coverage for edge cases including underscore-only inputs, mixed internal/trailing underscores, and non-alphanumeric character handling

Example

// Before: Both normalize to "Base"
naming.unify("Base_") // -> "Base"  
naming.unify("Base")  // -> "Base"  ❌ collision

// After: Trailing underscores preserved
naming.unify("Base_") // -> "Base_"
naming.unify("Base")  // -> "Base"  ✓ distinct

When these types reference the same group MyGroup, they now generate distinct names:

• Base_ + MyGroup → Base_MyGroup
• Base + MyGroup → BaseMyGroup

Original prompt

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This section details on the original issue you should resolve

<issue_title>Duplicate Names for Generated Groups</issue_title>
<issue_description>> Hey @Bergmann89,

Thanks for the response! I went ahead and created a minimal reproduction for the TypeAlreadyDefined bug based on the NeTEx schema issue we discussed. You can find the repo here: xsd_parser__type_already_defined_bug__minimal_reproduction.

The README explains how the collision happens when complexTypes differ only by a trailing underscore and both reference the same group. You can switch between the minimal schema and the real NeTEx XSDs using an environment variable.

Let me know if you have any questions or need more details!

Originally posted by @HelloJowet in #197</issue_description>

<agent_instructions>Verify if this is still an issue with the latest master branch</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Bergmann89 Maybe related to #138

• Fixes Duplicate Names for Generated Groups #207

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