Adds bytes read reporting for SDF.

[acrites]

SDF's SplittableProcessFn's report their backlog for autoscaling, so we need to also report their bytes processed for autoscaling to correctly compute time to clear backlog.

SplittableProcessFn's are tagged when constructing MapTaskExecutors and their output coders are attached to the ParDoOperation so the counter values can be updated while processing.

Also adds tests for the new code.

[github-actions]

📋 Review Summary

This PR enables reporting of bytes processed for Splittable DoFns (SplittableProcessFn) in the Dataflow streaming worker so that autoscaling can accurately estimate backlog clearance time alongside SDF backlog reporting. The implementation cleanly propagates the output coder to ParDoOperation, attaches the byte counter in ComputationWorkExecutorFactory, and aggregates the processed bytes in StreamingModeExecutionContext with thorough unit test coverage.

🔍 General Feedback

• The changes are well-structured, adhere to existing worker conventions, and include comprehensive unit tests across IntrinsicMapTaskExecutorFactoryTest, MapTaskExecutorTest, ComputationWorkExecutorFactoryTest, and StreamingModeExecutionContextTest.
• Calling getAndReset() on the shared Counter when multiple SDF ParDoOperations exist in the same MapTask works safely (since the first operation drains the shared counter and subsequent ones return 0), and the added comment in StreamingModeExecutionContext helpful documents the existing interaction with StreamingWorkerStatusReporter.

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[codecov]

Codecov Report

❌ Patch coverage is 90.69767% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.03%. Comparing base (76f6e6d) to head (293c6ac).
⚠️ Report is 215 commits behind head on master.

Files with missing lines	Patch %	Lines
...dataflow/worker/StreamingModeExecutionContext.java	90.00%	0 Missing and 2 partials ⚠️
...taflow/worker/IntrinsicMapTaskExecutorFactory.java	88.88%	0 Missing and 1 partial ⚠️
...low/worker/util/common/worker/MapTaskExecutor.java	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40639       +/-   ##
=============================================
+ Coverage     56.16%   76.03%   +19.86%     
- Complexity     2288     2301       +13     
=============================================
  Files          1124      259      -865     
  Lines        178336    14490   -163846     
  Branches       1489     1496        +7     
=============================================
- Hits         100170    11018    -89152     
+ Misses        75645     2766    -72879     
+ Partials       2521      706     -1815     

Flag	Coverage Δ
go	?
java	76.03% <90.69%> (+0.25%)	⬆️
python	?

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[github-actions]

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