Replace Scala Option with Java Optional

[kaklakariada]

Review follow-up from PR #394 for issue #393.

The Java production code still exposes or uses Scala Option in places such as StorageProperties. That keeps Scala interop visible in the Java implementation.

Proposed direction:

• Replace Scala Option with java.util.Optional in production APIs where possible.
• Keep conversions only at boundaries that still interact with Scala dependencies or tests.
• Update callers after the API change.