[FIX] defer check of file existence to workflow build stage

[bpinsard]

Attempt at fixing #400, that is still a blocker when parallelizing session processing with datalad.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.08%. Comparing base (13f7a1f) to head (8367ff3).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
sdcflows/fieldmaps.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #520      +/-   ##
==========================================
- Coverage   84.13%   84.08%   -0.06%     
==========================================
  Files          30       30              
  Lines        2874     2877       +3     
  Branches      380      382       +2     
==========================================
+ Hits         2418     2419       +1     
- Misses        381      382       +1     
- Partials       75       76       +1     

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[effigies]

LGTM. Thanks for looking into this, and apologies for letting it fall off the radar.

Have you tested this? Would it help to have an fMRIPrep image to test with? This can be backported trivially, so we can target pretty much any fMRIPrep series.

[bpinsard]

I am currently testing it on one of our dataset, patching a container with the file. It builds the workflow so it seems to work (though I have other unrelated issues with pre-computed derivatives).

[miltoncamacho]

LGTM