Refactored Fixed Experience Level Person Generation in Bulk Recruitment

[IllianiCBT]

This PR refactors the method by which we generate personnel at a fixed experience level during bulk recruitment. This was an option added a little while ago, but the implementation was... well, it wasn't great. Previously we looped until the right experience level was hit. This was possibly the most expensive way I could have accomplished the task and I've been looking for an excuse to redo it ever since it got merged.

Now, we just fetch the profession requested and then overwrite the randomized skill levels for that profession, replacing them with the fixed values. This is substantially quicker, and far more reliable than the earlier approach.

Closes #4579

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 10.31%. Comparing base (a684cf7) to head (1cd372a).
Report is 9 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4590      +/-   ##
============================================
- Coverage     10.31%   10.31%   -0.01%     
  Complexity     5818     5818              
============================================
  Files           936      936              
  Lines        128889   128964      +75     
  Branches      18960    18965       +5     
============================================
  Hits          13301    13301              
- Misses       114312   114387      +75     
  Partials       1276     1276              

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