feat: support enum-to-enum mapping with different properties

[wilmveel]

Summary

• Skip field resolution in the FIR checker when both source and target are enums with matching entry names, preventing false "Missing mapping for: label" errors
• Handle direct enum-to-enum mapping in the IR visitor (previously only worked for enum fields nested inside data classes)
• Add 4 new test cases covering enum mapping with extra properties (both as nested fields and direct mapping, in both directions)

Closes #14

Test plan

• shouldCompile_enumWithLabelProperty — maps data class with plain enum field to data class with labeled enum field
• shouldCompile_enumWithLabelPropertyReverse — reverse direction
• shouldCompile_directEnumWithLabelProperty — direct plain enum → labeled enum mapping
• shouldCompile_directEnumWithLabelPropertyReverse — direct labeled enum → plain enum mapping
• All existing tests pass (no regressions)

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