Deneb PR feedback updates (#4716)

* move length update outside of if let in LRU cache

* add comment and use hex for G1_POINT_AT_INFINITY

* remove some misleading comments from `ssz_snappy`

* make sure we can't overflow on blobs by range requests with large counts

* downgrade gossip verification internal availability check error

* change blob rpc responses from BlockingFnWithManualSendOnIdle to BlockingFn

* remove unnecessary collect in blobs by range response

* add a comment to blobs by range response start slot logic

* typo persist_data_availabilty_checker -> persist_data_availability_checker

* unify cheap_state_advance_to_obtain_committees

beacon_node/lighthouse_network/src/rpc/methods.rs

@@ -297,6 +297,12 @@ pub struct BlobsByRangeRequest {
     pub count: u64,
 }
 
+impl BlobsByRangeRequest {
+    pub fn max_blobs_requested<E: EthSpec>(&self) -> u64 {
+        self.count.saturating_mul(E::max_blobs_per_block() as u64)
+    }
+}
+
 /// Request a number of beacon block roots from a peer.
 #[superstruct(
     variants(V1, V2),