The processor appended sweeps the GUI fed back to its own history, so its next replay
published them twice and out of order, and the B-scan came out with rotated columns.
Fed-back sweeps now stay out of that history, results are kept in timestamp order,
picking the displayed combo only redraws and only new sweeps are recorded to disk.
The sar3d processor is rewritten as a checked port of Multi_antenna_3D_clean_v1.ipynb:
NVRTC kernels, timing from the trace stamps, notebook parameter names and one cubic
SAR_VOXEL_M. It adds front, side, top and 3D views, drops gpr_cpp and the parity tools,
and the GUI speed now applies only while the socket speed is ignored.