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/tests/test_gui_profile_codec.py

@@ -8,6 +8,7 @@ from python_app.models.gui_profile_model import (
     GuiPassThroughStateModel,
     GuiProcessingStateModel,
     GuiProfileModel,
+    GuiSar3dStateModel,
     GuiStateModel,
 )
 
@@ -53,6 +54,31 @@ class GuiProfileCodecTest(unittest.TestCase):
         twice = GuiProfileModel.from_dict(once).to_dict()
         self.assertEqual(once["gui"], twice["gui"])
 
+    def test_sar3d_section_round_trips(self) -> None:
+        sar3d = GuiSar3dStateModel(
+            input_positions="0,2",
+            output_positions="1,3",
+            min_depth_m=2.5,
+            max_depth_m=9.0,
+            start_freq_mhz=2000.0,
+            stop_freq_mhz=5500.0,
+            speed_m_s=1.42,
+            ignore_socket_speed_enabled=True,
+            look_angle_deg=6.5,
+            frame_radius=3,
+            voxel_m=0.035,
+            bp_ground_depth_m=1.1,
+            comp_range_power=0.5,
+            use_compensation=False,
+            normalize_each_frame=False,
+        )
+        profile = GuiProfileModel(gui=GuiStateModel(processing=GuiProcessingStateModel(sar3d=sar3d)))
+
+        decoded = GuiProfileModel.from_dict(profile.to_dict())
+
+        assert decoded.gui is not None
+        self.assertEqual(decoded.gui.processing.sar3d, sar3d)
+
     def test_missing_gui_section_yields_none(self) -> None:
         self.assertIsNone(GuiProfileModel.from_dict({}).gui)