[Scala Removal] Define Java user development API — FlinkStreamingJob lifecycle base class

[shangeyao]

Parent Issue

Part of #4408 — Remove Scala from StreamPark.

Implementation Track

Delivered in PR #4418 on branch feature/remove-scala.

Scope

Design and implement FlinkStreamingJob abstract base class in org.apache.streampark.flink.core.java package. Preserve lifecycle execution order: main → init → ready → handle → execute → destroy. Use Java DataStream API exclusively (Flink 1.17–1.20).

Estimated Files

~1 new Java file; replaces FlinkStreaming.scala

Dependencies

• Depends on [Build] Raise StreamPark compile and CI baseline to JDK 11 #4417 (JDK 11 baseline)

Acceptance Criteria

• FlinkStreamingJob compiles and lifecycle order matches Scala trait\n- [ ] handle() is abstract; ready(), destroy(), configure() have empty defaults\n- [ ] Migration note added to Javadoc

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Sub-issue 0.1 of Scala removal epic (#4408).