fix: harden typed metrics review findings

crates/crank-core/src/correlation.rs

@@ -183,6 +183,11 @@ impl TraceContext {
         &self.traceparent
     }
 
+    /// Whether this context was selected for recording by the upstream/local sampler.
+    pub fn is_sampled(&self) -> bool {
+        self.traceparent.ends_with("-01")
+    }
+
     pub fn tracestate_within_budget(value: &str) -> bool {
         header_list_within_budget(
             value,