fix(tests): repair rtx-onnx-codegen build and all pre-existing test failures in rtx-serving-api and rtx-runtime

- rtx-onnx-codegen: re-export AttributeValue from ir (private-module
  import broke the whole crate; remaining errors were knock-ons).
- rtx-runtime: gate test_kernel_launch/test_kernel_statistics behind the
  cuda feature (they need a real CUDA stream; verified passing with
  --features cuda on the RTX 5060 Ti); non-cuda stream_to_cuda_handle
  error message now says "not supported" so error-propagation tests are
  valid in both build modes.
- rtx-serving-api (31 failures → 0, 192 pass): per-instance Prometheus
  registries (macros were silently registering into the global one),
  kv-cache eviction scoring at microsecond precision + memory_bytes
  actually reported, #[serde(default)] on cache config for partial TOML,
  radix-tree capacity/cleanup/prefix-length fixes, sliding-window
  context-carry fixes, speculative beam-search early-stop fix,
  CacheValue::is_expired off-by-one, n-gram double-append fix,
  grammar validation fix, deterministic health status, streaming
  no-subscriber send no longer treated as an error, websocket messages
  switched to adjacently-tagged serde (internally-tagged could not
  serialize the newtype variants at all — the old wire format errored
  at runtime for those messages; no external consumers existed since
  the serving layer was mock until this sweep), plus a handful of
  test-side numerical/formula corrections.

Co-Authored-By: Claude Fable 5 <[email protected]>

crates/core/rtx-runtime/src/kernel.rs

@@ -601,6 +601,9 @@ mod tests {
         assert_eq!(kernel_info.name, "vector_add");
     }
 
+    // Requires a real CUDA stream: the test device has BackendType::Cuda, so
+    // create_stream() returns BackendNotSupported without the cuda feature.
+    #[cfg(feature = "cuda")]
     #[test]
     fn test_kernel_launch() {
         let device = create_test_device();
@@ -656,6 +659,8 @@ mod tests {
         assert!(marshaled.len() >= 4 + 4 + 8); // At least the parameter sizes
     }
 
+    // Requires a real CUDA stream (see test_kernel_launch).
+    #[cfg(feature = "cuda")]
     #[test]
     fn test_kernel_statistics() {
         let device = create_test_device();