[java][client] Emit @Email bean validation for string with format: email

[Ignacio-Vidal]

Adds @Email bean-validation support to the java client generator so that type: string / format: email properties and parameters are annotated with @Email, matching the behaviour in the Spring & jaxrs-spec generators (#24271).

Background

DefaultCodegen already sets isEmail = true for format: email schemas across every Java generator, but the java client's Java/beanValidationCore.mustache never consumed the flag. As a result, with useBeanValidation=true, an email field/parameter received @NotNull/@Size/@Pattern where applicable but never @Email — the validation was silently dropped.

Change

• No new import is required: javax/jakarta package is selected automatically due to import setup in the templates
• The clause is only reached under useBeanValidation, consistent with the existing constraints and is inherited b all libraries (native, jersey2/3, resttemplate, restclient, webclient, okhttp-gson, feign, retrofit2, microprofile)

PR checklist

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  Commit all changed files.
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Summary by cubic

Adds @Email bean validation to the Java client generator for type: string / format: email. Email properties and parameters are now annotated when useBeanValidation=true.

• New Features
  • Emit @Email in Java/beanValidationCore.mustache when isEmail is set; applies to all Java client libraries under useBeanValidation.
  • No import changes; existing wildcard imports jakarta.validation.constraints.* or javax.validation.constraints.* are used.
  • Added unit tests for jakarta/javax and the disabled case; regenerated the resttemplate-list-schema-validation sample with a User model (and @Email) and updated UserApi to return User as JSON.

^{Written for commit 6c6c91b. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 11 files

_{Re-trigger cubic}

[Ignacio-Vidal]

@wing328 - could you review this PR which is analogue to #24271?