pack_sim: Support the OPM Flow keyword PYACTION

[vkip]

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 41.17647% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.27%. Comparing base (f19cbac) to head (464abec).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
src/subscript/pack_sim/pack_sim.py	41.17%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #802      +/-   ##
==========================================
- Coverage   85.38%   85.27%   -0.11%     
==========================================
  Files          49       49              
  Lines        7539     7553      +14     
==========================================
+ Hits         6437     6441       +4     
- Misses       1102     1112      +10     

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[alifbe]

Cool 👍

The changes looks good to me. Could you please add a test case as well?