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/models/run_config_codec.py

@@ -219,6 +219,16 @@ def run_config_from_dict(payload: dict[str, Any]) -> RunConfigModel:
         "recovery_attempts",
         model.radar.multi_device.recovery_attempts,
     )
+    model.radar.multi_device.output_switch_positions = _read_int(
+       multi_device_payload,
+       "output_switch_positions",
+       model.radar.multi_device.output_switch_positions,
+    )
+    model.radar.multi_device.input_switch_positions = _read_int(
+           multi_device_payload,
+           "input_switch_positions",
+           model.radar.multi_device.input_switch_positions,
+        )
     model.radar.kamil_adc.project_dir = _read_str(
         kamil_adc_payload, "project_dir", model.radar.kamil_adc.project_dir
     )
@@ -493,6 +503,8 @@ def run_config_to_dict(model: RunConfigModel) -> dict[str, Any]:
                 "slave_serials": list(model.radar.multi_device.slave_serials),
                 "force_external_reference": model.radar.multi_device.force_external_reference,
                 "recovery_attempts": model.radar.multi_device.recovery_attempts,
+                "output_switch_positions": model.radar.multi_device.output_switch_positions,
+                "input_switch_positions": model.radar.multi_device.input_switch_positions
             },
             "kamil_adc": {
                 "project_dir": model.radar.kamil_adc.project_dir,