[ty_test] Extract HoverOutput type from CheckOutput enum
Create a dedicated HoverOutput struct to hold hover result data,
replacing the inline fields in CheckOutput::Hover variant.
This allows implementing Unmatched and UnmatchedWithColumn traits
directly on HoverOutput, simplifying the CheckOutput implementations
to simple delegation.
Benefits:
- Better separation of concerns
- Cleaner trait implementations
- More consistent with Diagnostic handling
- Easier to extend HoverOutput in the future
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Co-Authored-By: Claude <noreply@anthropic.com>
