Fix ThreadSafeDouble, ThreadSafeLong

Author: phnx47

src/Prometheus.Client/Internal/ThreadSafeDouble.cs

@@ -26,12 +26,13 @@ public void Add(double increment)
         {
             while (true)
             {
-                long initialValue = _value;
-                double computedValue = BitConverter.Int64BitsToDouble(initialValue) + increment;
+                var initialValue = Interlocked.Read(ref _value);
+                var computedValue = BitConverter.Int64BitsToDouble(initialValue) + increment;
 
                 if (initialValue == Interlocked.CompareExchange(ref _value, BitConverter.DoubleToInt64Bits(computedValue), initialValue))
                     return;
             }
+
         }
 
         public override string ToString()

src/Prometheus.Client/Internal/ThreadSafeLong.cs

@@ -23,14 +23,7 @@ public long Value
 
         public void Add(long increment)
         {
-            while (true)
-            {
-                long initialValue = _value;
-                long computedValue = initialValue + increment;
-
-                if (initialValue == Interlocked.CompareExchange(ref _value, computedValue, initialValue))
-                    return;
-            }
+            Interlocked.Add(ref _value, increment);
         }
 
         public override string ToString()