Add kaya-otel package for OpenTelemetry tracing and metrics

Instrument HTTP requests and WebSocket connections via Kaya hooks, covering both ASGI and RSGI. Records handler exceptions, WebSocket close codes, optional header capture, exclusions and lifecycle hooks.

Add route-template resolution and exception visibility to kaya-core so trace/metric attributes can use low-cardinality routes and failed spans can record escaped exceptions.

requirements-dev.in

@@ -7,6 +7,7 @@ kaya-oidc @ file:./packages/kaya-oidc
 kaya-openapi @ file:./packages/kaya-openapi
 kaya-cors @ file:./packages/kaya-cors
 kaya-forwarded @ file:./packages/kaya-forwarded
+kaya-otel @ file:./packages/kaya-otel
 build
 fakeredis
 mypy