[WIP] Type filtering for classes, enums, interfaces

[Copilot]

Implement type filtering for classes, enums, and interfaces. Adding the following methods to TypeFilters:

• Understand codebase structure and patterns
• Create TypeFilters.WhichAreClasses.cs with WhichAreClasses() and WhichAreNotClasses() methods
• Create TypeFilters.WhichAreEnums.cs with WhichAreEnums() and WhichAreNotEnums() methods
• Create TypeFilters.WhichAreInterfaces.cs with WhichAreInterfaces() and WhichAreNotInterfaces() methods
• Add comprehensive tests for each new filter method (6 tests total)
• Validate all tests pass (1495 tests including 6 new ones)
• Run API compatibility checks to ensure no breaking changes
• Create manual validation test to verify functionality

This implementation follows the existing patterns in the codebase, using the same Filter.Prefix approach and type checking logic found in the existing type assertion methods. All existing tests continue to pass.

Fixes #111.

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[vbreuss]

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