consensus: fix span handling in BlockVerifier

The BlockVerifier constructed a tracing span and manually entered it
inside of an async block.  Manually entering spans inside async blocks
can cause problems where the span might not be entered and exited
correctly as the resulting future is polled.  Instead, using the
.instrument creates a wrapper future that handles the bookkeeping.

I changed the span name and contents to be consistent with the spans in
the checkpoint verifier.

zebra-consensus/src/block.rs

@@ -19,6 +19,7 @@ use futures::stream::FuturesUnordered;
 use futures_util::FutureExt;
 use thiserror::Error;
 use tower::{Service, ServiceExt};
+use tracing::Instrument;
 
 use zebra_chain::{
     block::{self, Block},
@@ -114,14 +115,14 @@ where
         let mut transaction_verifier = self.transaction_verifier.clone();
         let network = self.network;
 
+        // We don't include the block hash, because it's likely already in a parent span
+        let span = tracing::debug_span!("block", height = ?block.coinbase_height());
+
         // TODO(jlusby): Error = Report, handle errors from state_service.
         async move {
+            tracing::trace!("beginning block verification");
+
             let hash = block.hash();
-
-            // The height is already included in the ChainVerifier span
-            let span = tracing::debug_span!("BlockVerifier::call", ?hash);
-            let _entered = span.enter();
-
             // Check that this block is actually a new block.
             match state_service
                 .ready_and()
@@ -200,6 +201,7 @@ where
                 _ => unreachable!("wrong response for CommitBlock"),
             }
         }
+        .instrument(span)
         .boxed()
     }
 }