[csharp][generichost] Fix invalid implicit cast

[devhl-labs]

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Summary by cubic

Fix C# GenericHost models to use Option.Value in property getters for optional fields. This removes invalid implicit casts and makes generated clients compile cleanly.

• Bug Fixes
  • Updated C# generichost model template (modelGeneric.mustache) so getters return the underlying value, not the Option<> wrapper.
  • Regenerated C# Petstore samples to reflect the change.

^{Written for commit 99c8478. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1129 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed.