chore: update lance-core dependency to v4.0.0-beta.7

[lance-community]

Summary

• Update lance-core.version in java/pom.xml from 2.0.0 to 4.0.0-beta.7.
• Keep the change scoped to the dependency version bump only.

Verification

• Ran cd java && make lint (pass).
• Ran cd java && make build.
• make build initially failed because org.lance:lance-core:4.0.0-beta.7 was not available from Maven Central on this runner.
• Installed the tagged source artifact locally for verification using:
  • git clone https://github.com/lance-format/lance.git
  • git checkout v4.0.0-beta.7
  • cd java && mvn -DskipTests -Dskip.build.jni=true install
• Re-ran cd java && make build (pass).

Triggering tag

• refs/tags/v4.0.0-beta.7