Add ProtocolFeatureStore cache in DriverChannel

No need to pull this information all the time from the channel.
Let's cache it when it is populated to the channel and use it.

Author: dkropachev

core/src/main/java/com/datastax/oss/driver/internal/core/channel/DriverChannel.java

@@ -76,6 +76,7 @@ public class DriverChannel {
   private final ProtocolVersion protocolVersion;
   private final AtomicBoolean closing = new AtomicBoolean();
   private final AtomicBoolean forceClosing = new AtomicBoolean();
+  private ProtocolFeatureStore featureStore;
 
   DriverChannel(
       EndPoint endPoint,
@@ -146,18 +147,35 @@ public Map<String, List<String>> getOptions() {
     return channel.attr(OPTIONS_KEY).get();
   }
 
+  public ProtocolFeatureStore getSupportedFeatures() {
+    if (featureStore != null) {
+      return featureStore;
+    }
+
+    ProtocolFeatureStore fromChannel = ProtocolFeatureStore.loadFromChannel(channel);
+    if (fromChannel == null) {
+      return ProtocolFeatureStore.Empty;
+    }
+    // Features can't be renegotiated.
+    // Once features is populated into channel it is enough to update cache and no need to
+    // invalidate it further.
+
+    featureStore = fromChannel;
+    return featureStore;
+  }
+
   public int getShardId() {
-    ConnectionShardingInfo info = ProtocolFeatureStore.loadFromChannel(channel).getShardingInfo();
+    ConnectionShardingInfo info = getSupportedFeatures().getShardingInfo();
     return info != null ? info.shardId : 0;
   }
 
   public ShardingInfo getShardingInfo() {
-    ConnectionShardingInfo info = ProtocolFeatureStore.loadFromChannel(channel).getShardingInfo();
+    ConnectionShardingInfo info = getSupportedFeatures().getShardingInfo();
     return info != null ? info.shardingInfo : null;
   }
 
   public LwtInfo getLwtInfo() {
-    return ProtocolFeatureStore.loadFromChannel(channel).getLwtFeatureInfo();
+    return getSupportedFeatures().getLwtFeatureInfo();
   }
 
   /**

core/src/main/java/com/datastax/oss/driver/internal/core/protocol/ProtocolFeatureStore.java

@@ -14,6 +14,8 @@ public class ProtocolFeatureStore {
   private final ShardingInfo.ConnectionShardingInfo shardingInfo;
   private final TabletInfo tabletInfo;
 
+  public static final ProtocolFeatureStore Empty = new ProtocolFeatureStore(null, null, null);
+
   ProtocolFeatureStore(
       LwtInfo lwtInfo, ShardingInfo.ConnectionShardingInfo shardingInfo, TabletInfo tabletInfo) {
     this.lwtInfo = lwtInfo;