[Task]: Move BundleLifter to sdk/util and reuse it in WriteFiles #40976

What needs to happen?

Follow-up to #40543.

(1) Move BundleLifter from Iceberg to sdks/java/core/.../sdk/util with @internal, keeping step names unchanged for Iceberg update compatibility.

(2) Make WriteFiles direct writes use it, which requires preserving each element's window/timestamp, a long threshold, and coder-based sizing.

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

Issue Components

• Component: Python SDK
• Component: Java SDK
• Component: Go SDK
• Component: Typescript SDK
• Component: IO connector
• Component: Beam YAML
• Component: Beam examples
• Component: Beam playground
• Component: Beam katas
• Component: Website
• Component: Infrastructure
• Component: Spark Runner
• Component: Flink Runner
• Component: Prism Runner
• Component: Hazelcast Jet Runner
• Component: Google Cloud Dataflow Runner