Fix telemetry resource export by adding rt-tokio feature

Without the rt-tokio feature on opentelemetry_sdk, the BatchSpanProcessor
silently fails to export resource attributes (service.name, service.instance.id)
with traces. This is a poorly designed API that compiles without errors but
produces broken behavior at runtime.

Changes:
- Add rt-tokio feature to opentelemetry_sdk dependency
- Re-enable AdaptiveSpanProcessor for tail-based sampling
- Add comment explaining rt-tokio requirement
- Bump version to 0.13.4

The issue only affected traces; logs and metrics were unaffected because
they use different code paths (with_batch_exporter for logs works differently).

Author: max-lt

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "openworkers-runner"
-version = "0.13.3"
+version = "0.13.4"
 edition = "2024"
 license = "MIT"
 default-run = "openworkers-runner"
@@ -48,7 +48,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 opentelemetry = { version = "0.31", optional = true }
 opentelemetry-otlp = { version = "0.31", features = ["grpc-tonic", "tls-roots"], optional = true }
 tonic = { version = "0.14", optional = true }
-opentelemetry_sdk = { version = "0.31", optional = true }
+opentelemetry_sdk = { version = "0.31", features = ["rt-tokio"], optional = true }
 tracing-opentelemetry = { version = "0.32", optional = true }
 opentelemetry-appender-tracing = { version = "0.31", features = ["experimental_use_tracing_span_context"], optional = true }
 sqlx = { version = "0.8.6", features = [ "runtime-tokio", "postgres", "uuid", "bigdecimal", "rust_decimal" ] }

Cargo.toml

@@ -138,6 +138,7 @@ fn init_otel() -> Result<(), Box<dyn std::error::Error>> {
     );
 
     // Create tracer provider
+    // Note: Requires rt-tokio feature on opentelemetry_sdk for proper resource export
     let tracer_provider = SdkTracerProvider::builder()
         .with_resource(resource.clone())
         .with_span_processor(adaptive_processor)