Copyfile_workflow conflicting filenames bugfix

[tclose]

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Summary

Handles the case where workflow outputs from separate fields have clashing filenames, e.g. "out_file.nii.gz". Filenames are disambiguated by appending a counter of the form ' (n).' to the filename.

Checklist

• I have added tests to cover my changes (if necessary)
• I have updated documentation (if necessary)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.25%. Comparing base (9b14a72) to head (3d1c21c).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #855      +/-   ##
==========================================
- Coverage   88.27%   88.25%   -0.03%     
==========================================
  Files          86       86              
  Lines       18009    18027      +18     
  Branches     3514     3517       +3     
==========================================
+ Hits        15898    15910      +12     
- Misses       1730     1736       +6     
  Partials      381      381              

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