[prism] Timer Clearing

[lostluck]

At least one of the Python tests test_pardo_timers_clear uses timer clearing.

/home/rebo/sdk/go1.22.1/bin/go build ../go/cmd/prism/*.go && python3 -m pytest -v apache_beam/runners/portability/prism_runner_test.py::PrismRunnerTest::test_pardo_timers_clear --test-pipeline-options="--environment_type=LOOPBACK --prism_bin=/home/rebo/git/beam/sdks/python/prism"

Most of this should already exist, but it's not fully supported in prism yet. It should be a matter of indicating how to write the "cleared" timer to the element manager in triageTimers.

[lostluck]

It's looking like I'm mis-handling the timer format!

From the Data stream, the Elements_Timers.Timers field is an encoded "logical stream" of timers.

That is there can be more than one. I'm treating that as a single timer, when there could in fact be more than one.

Need to add a decoding loop, but should help resolve the whole set.

This is in test_pardo_timers (without the clearing).

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The clear test has perplexing behavior though, as it looks like timers are simply never received. That can't be right.