[lake] Iceberg 1.12 plugin #4592

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• I searched in the issues and found nothing similar.

Description

• Replace the removed GenericAppenderFactory with GenericFileWriterFactory.
• Set the classloader for FormatModelRegistry.
• Fail clearly on Java < 17 and on old split state.
• Reject format v3 for primary-key tables.
• Surface cleanup failures.
• Align relocations with iceberg-flink-runtime and add the module's own NOTICE.

Willingness to contribute

• I'm willing to submit a PR!