Socket routing improvements, unit test cleanup (#276)

Updated WebSocket message routing improving performance for scenarios with multiple different subscriptions and topics
Added AddCommaSeparated helper for Enum value arrays to ParameterCollection
Improved EnumConverter performance and removed string allocation for happy path
Fixed CreateParamString extension method for ArrayParametersSerialization.Json
Fixed Shared GetOrderBookOptions and GetRecentTradeOptions base validations not being called

CryptoExchange.Net.UnitTests/Implementations/TestCredentials.cs

@@ -0,0 +1,30 @@
+using CryptoExchange.Net.Authentication;
+using System;
+
+namespace CryptoExchange.Net.UnitTests.Implementations
+{
+    internal class TestCredentials : HMACCredential
+    {
+        public TestCredentials() { }
+
+        public TestCredentials(string key, string secret) : base(key, secret)
+        {
+        }
+
+        public TestCredentials(HMACCredential credential) : base(credential.Key, credential.Secret)
+        {
+        }
+
+        public TestCredentials WithHMAC(string key, string secret)
+        {
+            if (!string.IsNullOrEmpty(Key)) throw new InvalidOperationException("Credentials already set");
+
+            Key = key;
+            Secret = secret;
+            return this;
+        }
+
+        /// <inheritdoc />
+        public override ApiCredentials Copy() => new TestCredentials(this);
+    }
+}