Port preprocessing workflow to NHP-dwiproc

[kaitj]

This PR makes the following changes:

• Ports the preprocessing workflow for HARDI sequences using the FSL distortion correction method for single + opposite phase encoding acquisitions.
• Fixes a previous bug with generating the phase encoding direction file, which was not quite correct in how the index was selected
• Fixes package building with uv + hatch
• Various bug fixes related to styx