[#24789][prism] Add testdofns for later

[lostluck]

Add the test DoFns used for bootstrap testing of prism. Unused in this PR.

These are used in the main pipeline tests for the runner, but aren't very interesting themselves.

A separate suit covers complex DoFns WRT "separation", like SDFs, process continuation and watermark estimating.

See #24789 for more information.

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[codecov]

Codecov Report

Merging #25557 (ee80586) into master (6667eb4) will decrease coverage by 0.13%.
The diff coverage is 1.70%.

❗ Current head ee80586 differs from pull request most recent head d37074b. Consider uploading reports for the commit d37074b to get more accurate results

@@            Coverage Diff             @@
##           master   #25557      +/-   ##
==========================================
- Coverage   72.64%   72.51%   -0.13%     
==========================================
  Files         763      764       +1     
  Lines      101060   101236     +176     
==========================================
  Hits        73413    73413              
- Misses      26226    26401     +175     
- Partials     1421     1422       +1     

Flag	Coverage Δ
go	52.03% <1.70%> (-0.29%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ks/go/pkg/beam/runners/prism/internal/testdofns.go	1.70% <1.70%> (ø)
...o/pkg/beam/runners/prism/internal/worker/worker.go	63.42% <0.00%> (-1.17%)	⬇️
...python/apache_beam/runners/worker/worker_status.py	74.66% <0.00%> (-0.67%)	⬇️
sdks/python/apache_beam/transforms/combiners.py	93.05% <0.00%> (-0.39%)	⬇️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.46% <0.00%> (+0.15%)	⬆️
...hon/apache_beam/runners/worker/bundle_processor.py	94.33% <0.00%> (+0.23%)	⬆️

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[lostluck]

R: @johannaojeling

This one is what it says on the tin. A bunch of Test DoFns that will eventually migrate into just the test file itself, instead of living in the package.

Having them in the "production" part of the package simplifies getting coverage numbers while iterating, and ensuring the different methods on the DoFns are activated as expected. Once metrics support in the runner is sufficiently robust, that can be changed to using counters and similar.

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[johannaojeling]

LGTM!