fix(engine): add await_state_root span to timeout path (#22111)

Co-authored-by: Amp <amp@ampcode.com>

crates/engine/tree/src/tree/payload_validator.rs

@@ -907,6 +907,12 @@ where
     /// Returns `ProviderResult<Result<...>>` where the outer `ProviderResult` captures
     /// unrecoverable errors from the sequential fallback (e.g. DB errors), while the inner
     /// `Result` captures parallel state root task errors that can still fall back to serial.
+    #[instrument(
+        level = "debug",
+        target = "engine::tree::payload_validator",
+        name = "await_state_root",
+        skip_all
+    )]
     fn await_state_root_with_timeout<Tx, Err, R: Send + Sync + 'static>(
         &self,
         handle: &mut PayloadHandle<Tx, Err, R>,