fix: Fix rust-server model generation following serde_valid upgrade

[dsteeley]

Add additional models to rust-server validation support following the upgrade to serde_valid 2.0. Also remove some duplicate #[cfg_attr(feature = "validate", validate)] .

I've attempted to reconcile the whitespace differences but leaving as I've not got further time to spend on this. I don't think they result in any functional changes.

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Summary by cubic

Fixes rust-server model generation after upgrading to serde_valid 2.0 by adding required composited validation support and removing duplicate validate attributes. Restores clean compilation and tidier generated code.

• Bug Fixes
  • Implemented serde_valid::validation::ValidateCompositedMinLength for newtype models when the validate feature is enabled.
  • Prevented duplicate #[cfg_attr(feature = "validate", validate)] on fields by guarding nested validation emission and placing the validate partial once for both required and optional fields.
  • Regenerated rust-server samples; removes duplicate validate attributes and includes minor whitespace-only changes.

^{Written for commit 0554ae7. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files