Reduce size of futures in HTTP API to prevent stack overflows (#5104)

* Box::pin a few big futures

* Arc the blocks early in publication

* Fix more tests

beacon_node/beacon_chain/src/data_availability_checker/overflow_lru_cache.rs

@@ -952,7 +952,7 @@ mod test {
         };
 
         let availability_pending_block = AvailabilityPendingExecutedBlock {
-            block: Arc::new(block),
+            block,
             import_data,
             payload_verification_outcome,
         };