Add real switch support for multi-device matrix radar

MultiDeviceLibreVnaService only exposes the 2x4 virtual combo matrix on
its own USB transport. When a physical GPIO switch sits on the master
stimulus and/or slave receiver path, the effective matrix is wider than
that. SwitchedMatrixRadarService wraps the inner service and drives the
extra switch(es) between acquire_collection calls, widening the combo
matrix by the physical position counts (matrix_output_switch_positions /
matrix_input_switch_positions in RunConfigModel).

Combo-matrix construction was centralized into
RunConfigModel.build_runtime_combos() so the GUI, workflows, and codec
all derive the same widened matrix instead of each computing its own
version of the virtual 2x4 layout.

python_app/workflows/sequential_capture_workflow.py

@@ -64,11 +64,7 @@ class SequentialCaptureSession:
         self._manual_matrix_radar_capture = (
             self._is_matrix_radar and kind in MATRIX_RADAR_MANUAL_CAPTURE_KINDS
         )
-        self._combos = (
-            RunConfigModel.build_matrix_radar_virtual_combos()
-            if self._is_matrix_radar
-            else RunConfigModel.build_full_combos(config.input_switch.positions, config.output_switch.positions)
-        )
+        self._combos = config.build_runtime_combos()
         if not self._combos:
             raise RuntimeError("No switch combinations available for capture")