[Drain] OnTimer - propagate caused by drain bit up to DoFnRunner

[stankiewicz]

Stacked on top of https://github.com/apache/beam/pull/37009

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[stankiewicz]

For stack delta, you look at relevant commit - ontimer

[gemini-code-assist[bot]]

Summary of Changes

Hello @stankiewicz, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Apache Beam Java SDK's timer mechanism by introducing a causedByDrain flag. This flag allows DoFns to distinguish between timers that fire as part of normal pipeline execution and those that are explicitly triggered during a pipeline draining process. By propagating this information through the core timer interfaces and their implementations, it provides more granular control and context for DoFns reacting to timer events, which is crucial for robust pipeline shutdown and data consistency during draining.

Highlights

• Propagate 'causedByDrain' Flag: Introduced a boolean causedByDrain parameter to the DoFnRunner.onTimer method and TimerInternals.TimerData to indicate if a timer firing was triggered by a draining operation.
• DoFn Context Updates: Added causedByDrain() abstract methods to DoFn.ProcessContext and DoFn.OnTimerContext to expose the drain status to user DoFn logic.
• Extensive Integration: Updated numerous DoFnRunner implementations, TimerData factory methods, and Timer utility classes across various runners (Core Java, Flink, Dataflow, Samza, Spark) and SDK components to correctly pass and handle the new causedByDrain flag.
• Test Coverage: Modified existing test cases to accommodate the new causedByDrain parameter in TimerData.of and Timer.of calls, ensuring consistency and correctness.

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[stankiewicz]

Run Java PreCommit