Hardened cluster-request deduplication (#2041)

* Harden cluster request deduplication by keeping a sliding window of last processed timestamps.

* Bump default deduplication window to 1 min.

src/Proto.Actor/Deduplication/DeduplicationContext.cs

@@ -72,6 +72,8 @@ public async Task DeDuplicate(MessageEnvelope envelope, Func<Task> continuation)
             if (IsDuplicate(key!, cutoff))
             {
                 _logger.LogInformation("Request de-duplicated");
+                // Update timestamp to keep a sliding window of TTL
+                _processed[key!]= now;
 
                 return;
             }

src/Proto.Cluster/ClusterConfig.cs

@@ -43,7 +43,7 @@ private ClusterConfig(string clusterName, IClusterProvider clusterProvider, IIde
         GossipFanout = 3;
         GossipMaxSend = 50;
         HeartbeatExpiration = TimeSpan.Zero;
-        ClusterRequestDeDuplicationWindow = TimeSpan.FromSeconds(30);
+        ClusterRequestDeDuplicationWindow = TimeSpan.FromMinutes(1);
         IdentityLookup = identityLookup;
         MemberStrategyBuilder = (_, _) => new SimpleMemberStrategy();
         RemotePidCacheTimeToLive = TimeSpan.FromMinutes(15);