Feature #2724 mode_openmp

[JohnHalleyGotway]

Expected Differences

This PR includes the following changes:

1. Update User's Guide with info about OpenMP in MODE.
2. Refine DataPlane debug functions to make them loop over the data more efficiently and refine their log messages.
3. Enhance interest.cc:

• Do the convolution step much more efficiently by updating the algorithm and including OpenMP.
• Update the SingleFeature class to store a pointer to the split field rather than mask field for each object.

4. Enhance engine.cc:

• Stop allocating a full grid of memory for each objects by operating on the SingleFeature split field rather than the mask field.
• Implement major changes to do_fcst/obs_merge_thresh() function to avoid memory allocation using a map of simple object to cluster ids and vice-versa.

5. Remove OpenMP from ensemble_stat.cc since it isn't actually used there anymore.

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

• Describe testing already performed for these changes:
  

  • Ran some timing tests for MODE using the 3km CONUS HRRR grid, as described in this issue comment. The enhanced convolution algorithm, along with OpenMP improve the runtime.
  • Ran this GHA run during development to confirm that no diffs are introduced.

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

  • @davidalbo, please confirm that the GHA run for this PR flags no diffs and review the logic of the code changes.
  • @hertneky, please review the doc updates and code changes, as you'd like.

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

  • Added MODE to the list of tools for which OMP_NUM_THREADS can be set.
  • Removed Ensemble-Stat from that list since it no longer computes NMEP.

• Do these changes include sufficient testing updates? [Yes]

  • I made no testing changes. I could set OMP_NUM_THREADS for MODE, but we're already doing a NP = 0 vs 2 for Grid-Stat. I don't think we need to do the same for MODE.

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [Tues Nov 7].
  

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[davidalbo]

I approve this pull request. I didn't go over this in great detail, the changes look pretty significant. All the unit tests did run successfully, it seems, and your changes are all compatible with those parts of the mode code that I am also modifying. Maybe you can go over what you did with me at some point, so I can learn more. For example you added a 'split' input to SingleFeature::set(), for (I'm sure) a good reason.