Add dr-inference-engine and route every model session through it

One crate names the runtime, the providers and the devices; dr-face and
dr-segment ask it for a session by role. It hands ort an API table once
per process — from a libonnxruntime it dlopens when the app names a
directory holding one, otherwise from tract — so the Rust build stays
free of C on every target and a package can install the runtime as a
file (docs/inference.md §3).

Sessions live in a registry behind a Model handle that holds the bytes,
not the session: every use refreshes a timestamp and a reaper unloads
whatever sat idle past the decay. A scan that runs the detector on each
image never lets it go idle; a click in the develop view lets the
segmenter go after thirty seconds; a handle used after that reloads,
and reloads on a higher rung if a compiled engine has landed meanwhile.

The probe walks the platform's ladder by building strict sessions and
timing them against the CPU provider, caches the choice against a
fingerprint of the runtime, driver, hardware and models, and compiles
engines for the selected rung in the background, smallest model first.
Nothing in this commit turns the native path on: the apps still run on
tract until they call init with a runtime directory.

core/dr-face/Cargo.toml

@@ -9,10 +9,11 @@ license.workspace = true
 thiserror.workspace = true
 log.workspace = true
 
-# Inference. `ort` is the API; **tract is the engine** — see the workspace
-# manifest, and docs/faces.md §3, for why the C++ ONNX Runtime is not linked.
+# Inference. `ort` is the API; **what runs it is `dr-inference-engine`'s
+# business** — tract, or an ONNX Runtime the app found on disk, on whichever
+# provider the device has (docs/inference.md). This crate never names either.
 ort = { workspace = true, optional = true }
-ort-tract = { workspace = true, optional = true }
+dr-inference-engine = { workspace = true, optional = true }
 ndarray = { workspace = true, optional = true }
 
 [dev-dependencies]
@@ -20,7 +21,7 @@ zune-jpeg.workspace = true
 env_logger.workspace = true
 # The M1 probe drives `ort` directly so it can print the raw load error.
 ort = { workspace = true }
-ort-tract = { workspace = true }
+dr-inference-engine = { workspace = true }
 
 [[example]]
 name = "probe"
@@ -48,4 +49,4 @@ default = []
 # must be testable against synthetic embeddings on a machine with no weights on
 # it — a test suite that needs a research-licensed download is a test suite
 # that does not run in CI.
-inference = ["dep:ort", "dep:ort-tract", "dep:ndarray"]
+inference = ["dep:ort", "dep:dr-inference-engine", "dep:ndarray"]