RF: Switch from DerivativesDataSinks to Prep/Save nodes

[effigies]

Utilizing https://github.com/nipreps/niworkflows/pull/885. The goal here is to reduce unnecessary copies to the derivatives directory by doing any data transformation in a cached node, and then using an always_run node to check hashes and copy only if needed.

This should reduce the amount of rerunning done with --derivatives $MINIMAL.