Separate GPU class for a shifted MRT, all-blocked, stationary-body case
without Jets: window totals vs summed per-base reads (substep-scaled
tolerance), bitwise populations vs a raw-only stepper, a single step(N)
stepper with bitwise-equal window rows and populations, step(0)
non-change, and reset after a window. SRT/Jet test stays separately
scoped. Test-only.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>