`Radiation::filBndry` periodic path only fills one component, breaking multigroup boundary data

Location

Source/radiation/Radiation.cpp:1384, Source/radiation/Radiation.cpp:1391, Source/radiation/Radiation.cpp:1400, Source/radiation/Radiation.cpp:1408

Problem

In Radiation::filBndry, the non-periodic branch correctly handles Radiation::nGroups components, but the periodic branch allocates temporary MultiFabs with only 1 component and copies/combines only 1 component.

This is inconsistent with callers like getBndryDataMG() that pass a multigroup BndryRegister.

Impact

• For periodic domains with multigroup radiation (nGroups > 1), only group 0 coarse boundary data is filled.
• Remaining groups can stay stale/sentinel values, producing incorrect multigroup boundary conditions.

Steps to Reproduce

1. Run a multigroup (nGroups > 1) case with periodic boundaries that exercises coarse-fine radiation boundary fills.
2. Inspect coarse boundary register values after filBndry().
3. Observe only one group being populated.

Expected Behavior

Periodic and non-periodic branches should both fill all Radiation::nGroups components.

Actual Behavior

Periodic branch fills only one component.

Proposed Fix

Use Radiation::nGroups (or bdry.nComp()) consistently in periodic branch allocation/copy/linComb.

int ncomp = Radiation::nGroups;

if (need_old_data) {
    sold_tmp.define(grids, dmap, ncomp, n_grow);
    sold_tmp.setVal(0.0);
    MultiFab::Copy(sold_tmp, S_old, Rad, 0, ncomp, 0);
    sold_tmp.FillBoundary(geom.periodicity());
}

if (need_new_data) {
    snew_tmp.define(grids, dmap, ncomp, n_grow);
    snew_tmp.setVal(0.0);
    MultiFab::Copy(snew_tmp, S_new, Rad, 0, ncomp, 0);
    snew_tmp.FillBoundary(geom.periodicity());
}

if (time > new_time - eps) {
    bdry.copyFrom(snew_tmp, n_ghost, 0, 0, ncomp);
} else if (time < old_time + eps) {
    bdry.copyFrom(sold_tmp, n_ghost, 0, 0, ncomp);
} else {
    bdry.linComb(a, sold_tmp, 0, b, snew_tmp, 0, 0, ncomp, n_ghost);
}

Prepared by Codex

Start in Source/radiation/Radiation.cpp at the four filBndry locations listed in the issue, comparing the periodic and non-periodic branches. Trace the multigroup BndryRegister path through getBndryDataMG(). Done means periodic coarse-fine fills populate all Radiation::nGroups components, including interpolation between old and new data.