Give the engine an Inpainter role for the panorama border filler

MI-GAN is plain convolutions, so every rung serves it and none needs a
special form; the role exists so resolve_model and the probe's fingerprint
know the model, and so the merge job can open it through the engine rather
than tract, which takes 7.4 s a tile for it.

core/dr-inference-engine/src/lib.rs

@@ -41,6 +41,10 @@ pub enum Role {
     EyeClassifier,
     /// XFeat, the panorama keypoint detector (docs/panorama.md).
     Keypoints,
+    /// MI-GAN, the panorama border filler (docs/panorama.md §12). Plain
+    /// convolutions, so any rung serves it; fp16 on TensorRT and int8 on
+    /// the Hexagon are the point of it.
+    Inpainter,
 }
 
 /// Which numeric form of a model a session was built from.
@@ -94,7 +98,7 @@ impl Rung {
     }
 
     /// The model form this rung wants for a role.
-    fn form(self, role: Role) -> Form {
+    fn form(self, _role: Role) -> Form {
         match self {
             Rung::Hexagon => Form::Int8,
             _ => Form::F32,