Check that the ensemble exists for the specified iterations before calculating anything

[oddvarlia]

Purpose: Add a check that the ensemble on scratch disk has completed with the iterations specified in the config file for this script.
This is a workaround to ensure that the calculations of field parameter statistics are started before the final realizations are created. Using the HOOK_WORKFLOW with POST_SIMULATION will start the workflow after each iteration, not after all iterations are completed. This will trigger unnecessary runs of the calculation of field parameter statistics since the only meaningfull calculation is after the final iteration is completed. By adding this check, it is possible to avoid unnecessary calculations and waste of time. Ideally ERT should have an option for HOOK_WORKFLOW that start a workflow in ERT after all iterations are completed, but that is not available by the time of writing.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 85.80%. Comparing base (71ee493) to head (9748951).

Files with missing lines	Patch %	Lines
src/subscript/field_statistics/field_statistics.py	83.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #756      +/-   ##
==========================================
- Coverage   85.81%   85.80%   -0.01%     
==========================================
  Files          52       52              
  Lines        7318     7342      +24     
==========================================
+ Hits         6280     6300      +20     
- Misses       1038     1042       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alifbe]

LGTM 👍