#24348 Add integer enum tests to existing composed enum tests

a follow up pr to https://github.com/OpenAPITools/openapi-generator/pull/23869

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Summary by cubic

Add integer enum coverage to the C# generichost composed-enum tests. Adds TypeIntegerWithOneOf (int32 oneOf/const) and folds the old annotated enum sample into ComposedEnum.

• Refactors
  • Added TypeIntegerWithOneOf to the 3.0 composed-enum spec and generated sample; registered TypeIntegerWithOneOfJsonConverter.
  • Removed bin/configs/csharp-generichost-latest-annotatedEnum.yaml and the AnnotatedEnum sample; tests now live under ComposedEnum.
  • Updated docs, OpenAPI, and tests for the new integer enum.
  • Updated .github/workflows/samples-dotnet10.yaml to remove the deleted AnnotatedEnum sample from the CI matrix.