fix(core): Caches DateTime.NowUtc (#548)

- [X] Caches DateTime.NowUtc on the game loop (not other threads)
- [X] Replaces all locations where it makes sense
- [X] Adds Min/Max for `IComparable` (TimeSpan, DateTimes, etc)

Closes #261

Projects/Server/Serialization/BufferWriter.cs

@@ -205,6 +205,8 @@ namespace Server
             Write(ticks);
         }
 
+        // TODO: Find a way to speed this up.
+        // Maybe used a special cached value?
         public void WriteDeltaTime(DateTime value)
         {
             var ticks = (value.Kind switch

Projects/Server/Serialization/Persistence.cs

@@ -84,14 +84,14 @@ namespace Server
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteConsole(string message)
         {
-            var now = DateTime.UtcNow;
+            var now = Core.Now;
             Console.Write("[{0} {1}] Persistence: {2}", now.ToShortDateString(), now.ToLongTimeString(), message);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteConsoleLine(string message)
         {
-            var now = DateTime.UtcNow;
+            var now = Core.Now;
             Console.WriteLine("[{0} {1}] Persistence: {2}", now.ToShortDateString(), now.ToLongTimeString(), message);
         }
 
@@ -100,7 +100,7 @@ namespace Server
             try
             {
                 using var op = new StreamWriter("save-errors.log", true);
-                op.WriteLine("# {0}", DateTime.UtcNow);
+                op.WriteLine("# {0}", Core.Now);
 
                 op.WriteLine(ex);