[Java][Spring] Add examples parameter in @Schema annotation for OAS 3.1 spec

[peter-em]

Added handling of examples keyword for OAS 3.1 spec.
They are generated in the corresponding @Schema annotation, next to the singular example

Resolve #24755

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Summary by cubic

Adds support for the OAS 3.1 examples keyword so Java Spring generators emit it in the @Schema annotation alongside the singular example.

• Adds an examples property to CodegenProperty, populated from the schema's examples list via new toExampleValues / getExampleValueToString hooks that stringify scalar, array, and object values.
• Refactors AbstractJavaCodegen.toExampleValue so example and examples share the same string escaping and Date handling; error reporting is consolidated in handleExampleException.
• Updates the Java Spring pojo.mustache template to render examples = { ... } only when at least one value is present.
• Adds tests and a sample spec (issue_24755.yaml) covering string, integer, array, object, and empty examples lists.

Resolves #24755.

^{Written for commit d156fdc. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 6 files

<sub>Reply with feedback, questions, or to request a fix.

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[cubic-dev-ai]

All reported issues were addressed across 6 files (changes from recent commits).

<sub>Requires human review: Auto-approval blocked because this review re-detected 1 unresolved issue already reported by Cubic.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>

[peter-em]

There is already a PR for #24755 similar to this, but it has been inactive for a while now.
If examples support could be included in one of upcoming releases, it would be useful for my company's project, so I decided to create a new PR.