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/UOContent/Items/Weapons/BaseWeapon.cs

@@ -730,7 +730,7 @@ namespace Server.Items
 
                 if (canSwing)
                 {
-                    canSwing = !(attacker is PlayerMobile p) || p.PeacedUntil <= DateTime.UtcNow;
+                    canSwing = !(attacker is PlayerMobile p) || p.PeacedUntil <= Core.Now;
                 }
             }