Load the runtime that fits the GPU, not the first one found

A runtime carries one vendor's providers, only one loads per process,
and a device can now hold several: the package's OpenVINO or WebGPU
build, a CUDA build the user fetched, the distribution's ROCm build.
`api::install` opens each it finds, lists its providers with
GetAvailableProviders, and installs the one scoring highest against the
GPUs `hardware::detect` reads from files — a vendor rung on its own
vendor's GPU above OpenVINO on an Intel one above the generic WebGPU
rung above a CPU-only build. Equal scores keep the old first-found
order, and DARKROOM_ORT_DIR still wins outright. The losers stay mapped
rather than unloaded.

The Linux fingerprint now names the OpenCL drivers too, so installing
Intel's re-probes. `ladder` takes DARKROOM_ORT_DIRS to show the choice.

core/dr-inference-engine/examples/ladder.rs

@@ -6,6 +6,9 @@
 //!     cargo run --release -p dr-inference-engine --features native,tract \
 //!     --example ladder -- CACHE_DIR models/face/scrfd_500m_640.onnx [ROLE=MODEL.onnx ...]
 //!
+//! `DARKROOM_ORT_DIRS=a:b:c` offers several runtimes, as the app's search
+//! list does, and shows which the engine chose for this device's GPU.
+//!
 //! A bare path is a `Detector`; `denoiser=…`, `scene=…`, `inpainter=…`,
 //! `landmarks=…` (any `Role`, lower case) says otherwise, so a device can
 //! show each role taking its own form (inference.md §1.5). Each is opened
@@ -31,9 +34,16 @@ fn main() {
         std::process::exit(2);
     }
 
+    // DARKROOM_ORT_DIRS lists several, colon-separated, as the app's search
+    // does: the engine loads the one that fits the GPU (§3.2).
     let runtime_dirs: Vec<PathBuf> = std::env::var_os("DARKROOM_ORT_DIR")
         .map(PathBuf::from)
         .into_iter()
+        .chain(
+            std::env::var_os("DARKROOM_ORT_DIRS")
+                .map(|v| std::env::split_paths(&v).collect::<Vec<_>>())
+                .unwrap_or_default(),
+        )
         .collect();
     let started = Instant::now();
     dr_inference_engine::init(dr_inference_engine::Config {