sar3d: GPU port of the notebook with four views

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.

python_app/gui/app_window.py

@@ -371,9 +371,6 @@ class AppWindow(
         self._gpr_region_contours = []
         self._gpr_geometry_signature = None
         self._gpr_selected_geometry = None
-        self._sar3d_lookup_table = None
-        self._sar3d_xz_image_item = None
-        self._sar3d_xy_image_item = None
         self._phase_viewbox = None
         self._history_run_signature = None
         self._processor_run_signature = None