feat: Add support for SpaceMouse mod (6D input knob) (#1853)

Use `-DSPACEMOUSE=YES` CMake option to activate on Horus color targets.
Co-authored-by: Niel Horne (elecpower), Raphael Coeffic (raphaelcoeffic) and Peter Feerick (pfeerick).

radio/src/tests/conversions.cpp

@@ -427,7 +427,7 @@ TEST(Conversions, ConversionX12SFrom23)
   EXPECT_STRNEQ("Tes", g_model.telemetrySensors[0].label);
   EXPECT_EQ(10, g_model.telemetrySensors[0].id);
   EXPECT_EQ(9, g_model.telemetrySensors[0].frskyInstance.physID);
-  EXPECT_EQ((NUM_POTS + NUM_SLIDERS + 3), g_model.thrTraceSrc); // CH3
+  EXPECT_EQ(source2ThrottleSource(MIXSRC_CH3), g_model.thrTraceSrc); // CH3
 
   simuFatfsSetPaths("","");
 }