Fix filtering race condition

[knoepfel]

This PR fixes a data race in filtering, where a filter result was being sent multiple times for the same data cell. This PR also introduces unit tests that verify the expected filtering behavior.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
phlex/core/filter.cpp	0.00%	0 Missing and 3 partials ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (56.83%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   57.05%   56.83%   -0.23%     
==========================================
  Files         116      116              
  Lines        2580     2583       +3     
  Branches     1104     1105       +1     
==========================================
- Hits         1472     1468       -4     
- Misses        276      280       +4     
- Partials      832      835       +3     

Flag	Coverage Δ
unittests	56.83% <50.00%> (-0.23%)	⬇️

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Files with missing lines	Coverage Δ
phlex/core/detail/filter_impl.cpp	58.49% <100.00%> (+1.62%)	⬆️
phlex/core/detail/filter_impl.hpp	80.00% <ø> (-20.00%)	⬇️
phlex/core/filter.cpp	38.88% <0.00%> (-6.40%)	⬇️

... and 2 files with indirect coverage changes

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[greenc-FNAL]

This isn't the cause of the occasional test failure, is it?

[knoepfel]

This isn't the cause of the occasional test failure, is it?

Maybe. I know at least one of the benchmark tests that was failing (benchmark:09) was using filters. I haven't seen it fail with this fix. But I want to test it on scisoftbuild02; I've been testing on my Mac.

[knoepfel]

Maybe. I know at least one of the benchmark tests that was failing (benchmark:09) was using filters. I haven't seen it fail with this fix. But I want to test it on scisoftbuild02; I've been testing on my Mac.

I've tested this on scisoftbuild02 repeatedly, and not encountered any failures.

[wddgit]

Looks like it fixes the bug. There was one minor suggestion, but that is all I noticed.