Neokil fix/csharp test type name collision

[wing328]

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Summary by cubic

Qualifies model types in generated C# Generic Host API tests to avoid collisions with .NET types. Uses fully qualified model names in Assert.IsType checks so tests compile when model names match framework types.

• Bug Fixes
  • In csharp/libraries/generichost/api_test.mustache, Assert.IsType<> now prefixes model return types with {{packageName}}.{{modelPackage}} (only when isModel) to disambiguate.
  • Regenerated C# Generic Host samples across latest, net8, net10, net4.7, and net4.8 to apply the change.

^{Written for commit f07e31e. Summary will update on new commits.}