test: cover managed backfill commits on rest-dir

[hfutatzhanghb]

Summary

• Add an opt-in managed-versioning mode to the local REST directory namespace server.
• Forward the mode through make docker-test and the pytest REST fixture.
• Run the ADD COLUMNS and UPDATE COLUMNS backfill tests in a separate managed rest-dir Docker invocation so existing REST search tests keep their current server behavior.

Context

Follow-up to #772 and #772 (comment).

The existing backfill tests were REST-compatible, but no CI job selected them on rest-dir and the default directory adapter reported managedVersioning=false. The dedicated invocation enables both manifest_enabled and table_version_tracking_enabled, matching the managed-versioning setup covered by lance-core 11.0.0-beta.10.

Validation

• ./mvnw spotless:check -pl lance-spark-3.5_2.13 -am -DskipTests
• Standalone javac compilation of LanceRestDirNamespaceServer.java
• Python AST and workflow YAML parsing
• Pytest collection confirms exactly two managed backfill tests on rest-dir
• make -n docker-test confirms the managed-versioning flag reaches the container

The local host has no Docker CLI and its x86_64 JVM cannot load the available macOS JNI artifact, so the managed REST round-trip is delegated to the new Ubuntu Docker CI step.

[lance-gatekeeper]

✅ Gate recommendation: approve.

Both prior findings are fixed. The managed REST tests now distinguish namespace commits from direct dataset commits, and workflow filtering covers the Java and Scala production paths that control managed backfills.