Calculate byte size via sampling in StateBackedIterable if size is not cheap to calculate

[stankiewicz]

For Dataflow V2, StateBackedIterable is iterated by readers after gbk shuffle. Examples are ParDo after GBK or merging combiners after GBK.

metrics.proto specifies that Sampling is used because calculating the byte count involves serializing the elements which is CPU intensive.

In case of StateBackedIterable sampling is not occurring which impacts performance of some of the pipelines that have expensive coders.

This change introduces sampling.

Fully fixes #33620 as previous fix was improvement.

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[stankiewicz]

Run Java_PVR_Flink_Docker PreCommit

[stankiewicz]

flaky tests: https://develocity.apache.org/scans/tests?search.timeZoneId=Europe%2FWarsaw&tests.container=org.apache.beam.runners.dataflow.worker.windmill.client.grpc.GrpcDirectGetWorkStreamTest&tests.test=testConsumedWorkItems_itemsSplitAcrossResponses&tests.unstableOnly=false

https://develocity.apache.org/scans/tests?search.timeZoneId=Europe%2FWarsaw&tests.container=org.apache.beam.runners.dataflow.worker.streaming.harness.FanOutStreamingEngineWorkerHarnessTest&tests.test=testOnNewWorkerMetadata_redistributesBudget

[stankiewicz]

Run Java PreCommit