ENH: insert gradunwarp in bold workflow

[bpinsard]

Changes proposed in this pull request

The goal of that PR is to integrate gradient unwarping to the BOLD preprocessing workflows (and to anat workflows through update of smriprep). See https://github.com/nipreps/fmriprep/issues/1550. Relies on an updated version of the gradunwarp https://github.com/bpinsard/gradunwarp/tree/fix/mem_leaks.

Unwarping is applied on the initial ref (to use a single volume, it mainly takes into account the matrix size and affine rather than image content). Warp-field is then passed to the bold_bold, bold_T1w, bold_std one-step resamplings.

Still a WIP: inserting gradient unwarping seems more challenging for BOLD than for anatomical images. I need to check how that integrates with sdcflows.

Necessary PRs: https://github.com/nipreps/smriprep/pull/355 https://github.com/nipreps/niworkflows/pull/819

Documentation that should be reviewed

TODO: document the option to pass a gradient coeff file.

[codecov[bot]]

Codecov Report

Patch coverage: 36.36% and project coverage change: -0.14% :warning:

Comparison is base (e1c4bac) 49.29% compared to head (71845e5) 49.15%. Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3064      +/-   ##
==========================================
- Coverage   49.29%   49.15%   -0.14%     
==========================================
  Files          46       46              
  Lines        3593     3609      +16     
==========================================
+ Hits         1771     1774       +3     
- Misses       1822     1835      +13     

Files Changed	Coverage Δ
fmriprep/workflows/base.py	10.00% <ø> (-0.26%)	:arrow_down:
fmriprep/workflows/bold/base.py	19.84% <0.00%> (-0.71%)	:arrow_down:
fmriprep/workflows/bold/registration.py	10.63% <ø> (ø)
fmriprep/workflows/bold/resampling.py	11.20% <ø> (ø)
fmriprep/cli/parser.py	82.74% <100.00%> (+0.07%)	:arrow_up:
fmriprep/config.py	82.08% <100.00%> (+0.08%)	:arrow_up:

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