Fix: Cast Enum to integer when assigning to non-convertible types

- Update TypeConversionAnalyzer to only use EnumCastThenConversion if the target type is not an Enum and does not have a defined Conversions.To method.
- Add tests covering the reported issue (implicitly casting Enum to custom struct expecting int) and ensuring Enum-to-Boolean logic remains intact without extra (long) casts.

Co-authored-by: GrahamTheCoder <2490482+GrahamTheCoder@users.noreply.github.com>

Author: google-labs-jules[bot]