Use ProcessConfig rng to create VaryRun initial points

[timothy-nunn]

vary_iteration_variables was not using the randomly seed generator from ProcessConfig and was creating its own. This generator was not seeded from run_process.conf.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 46.30%. Comparing base (9e5012f) to head (3faac31).

Files with missing lines	Patch %	Lines
process/main.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4042      +/-   ##
==========================================
- Coverage   46.30%   46.30%   -0.01%     
==========================================
  Files         123      123              
  Lines       28962    28960       -2     
==========================================
- Hits        13411    13410       -1     
+ Misses      15551    15550       -1     

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