Fix pathfinder column order in draws()

[jgabry]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Brings pathfinder CSV reading more in line with other fitted model methods and ensures the order of diagnostic columns is now consistent with other fitted model methods.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Jonah Gabry

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.47%. Comparing base (df60989) to head (cc82e59).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1205   +/-   ##
=======================================
  Coverage   91.47%   91.47%           
=======================================
  Files          15       15           
  Lines        6155     6156    +1     
=======================================
+ Hits         5630     5631    +1     
  Misses        525      525           

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