Add fix_rbc_release_tr.py script for TR bandpass bug

Lets users of an RBC data release re-derive the cleaned BOLD with a
correctly-bandpassed `3dTproject`, by patching the template-space
`desc-head_bold.nii.gz` header (TR=0.0 on disk) with the TR read from
the native-space `desc-preproc_bold.nii.gz` header before regression.

Only the bandpass bug (#4 in docs/cpac_comparison.md) is addressed.
Downstream derivatives (ALFF, ReHo, atlas timeseries, connectivity)
are not regenerated; users wanting those should recompute from the
fixed BOLD with their own tooling.

Also promotes `_restore_tr` to a public `restore_tr` for reuse by
external tooling.

Author: nx10