Move the panorama keypoint detector onto the engine, and probe with a detector

XFeat's two exports are a Keypoints role now; the crate no longer names
tract, and the app compiles TensorRT engines for both ahead of the
first merge. The probe picks the smallest *detector* rather than the
smallest file: the tablet's first run chose the 112 KB eye classifier,
which has no int8 form, and reported the Hexagon as failed for want of
one.

core/dr-pano/src/lib.rs

@@ -63,3 +63,13 @@ pub enum PanoError {
     #[error("inference: {0}")]
     Inference(#[source] ort::Error),
 }
+
+#[cfg(feature = "xfeat")]
+impl From<dr_inference_engine::Error> for PanoError {
+    fn from(e: dr_inference_engine::Error) -> Self {
+        match e {
+            dr_inference_engine::Error::Inference(e) => PanoError::Inference(e),
+            dr_inference_engine::Error::Io(e) => PanoError::ModelRead(e),
+        }
+    }
+}