fix(mp7particledata): to_prp bug fix

[kallejahn]

Small fix to iteration in NodeParticleData.to_prp().

Added another iteration through nodedata, as previously iteration only passed through the first node, so total particles could only equal the number of subdivisions. With fix total particles now equals the number of nodes times the number of subdivisions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.4%. Comparing base (556c088) to head (65d1d53).
⚠️ Report is 146 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2737      +/-   ##
===========================================
+ Coverage     55.5%    72.4%   +16.9%     
===========================================
  Files          644      674      +30     
  Lines       124135   130670    +6535     
===========================================
+ Hits         68947    94684   +25737     
+ Misses       55188    35986   -19202     

Files with missing lines	Coverage Δ
flopy/modpath/mp7particledata.py	88.4% <100.0%> (+<0.1%)	⬆️

... and 570 files with indirect coverage changes

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[wpbonelli]

thanks @kallejahn !