Add encryption to namespace copy params

[JevonCowell]

What?

Add optional encryption support to NamespaceCopyFromParams so standalone copy operations can specify namespace encryption directly.

Why?

Users can currently work around this by using NamespaceWriteParams.copyFromNamespace(...) with top-level encryption(...), but adding encryption to NamespaceCopyFromParams makes the standalone copy operation support this convenience directly.

Risk evaluation (required)

Low. This adds an optional request body field and mirrors the existing NamespaceWriteParams encryption API. Existing requests without encryption continue to serialize the same required source_namespace fields.

How will the change get rolled back? (optional)

Revert this pull request.

Verification

• ./gradlew :turbopuffer-java-core:test --tests 'com.turbopuffer.models.namespaces.NamespaceCopyFromParamsTest'
• ./scripts/format
• git diff --check

[benesch]

Hey @JevonCowell, thanks for the PR. This idea makes sense. However, this SDK is automatically generated from our OpenAPI spec, so we can't accept this change as is! We need to update the upstream API spec instead. Let me see about getting that done for you.

[JevonCowell]

Done in #244