add error handling for missing L2 block (#430)

Author: frisitano

crates/chain-orchestrator/src/lib.rs

@@ -650,7 +650,7 @@ impl<
                     .get_block_by_number(block_number.into())
                     .full()
                     .await?
-                    .expect("L2 head block must exist")
+                    .ok_or(ChainOrchestratorError::L2BlockNotFoundInL2Client(block_number))?
                     .header
                     .hash_slow();
 
@@ -1015,7 +1015,9 @@ impl<
                 .get_block_by_number(current_head_block_number.into())
                 .full()
                 .await?
-                .expect("current head block must exist");
+                .ok_or(ChainOrchestratorError::L2BlockNotFoundInL2Client(
+                    current_head_block_number,
+                ))?;
 
             // If the timestamp of the received block is less than or equal to the current head,
             // we ignore it.
@@ -1077,7 +1079,7 @@ impl<
                     .get_block_by_number(header.number.into())
                     .full()
                     .await?
-                    .expect("block must exist")
+                    .ok_or(ChainOrchestratorError::L2BlockNotFoundInL2Client(header.number))?
                     .into_consensus()
                     .map_transactions(|tx| tx.inner.into_inner());