Allow random to be passed to PokemonBuilder build function, if none is passed use a static fallback.

PkmnLibSharp/Battling/PokemonBuilder.cs

@@ -11,6 +11,8 @@ namespace PkmnLibSharp.Battling
         where TPokemon : Pokemon 
         where TLearnedMove :LearnedMove
     {
+        private static readonly Random _defaultRandom = new Random();
+        
         protected readonly BattleLibrary Library;
         public string Species { get; }
         public string Forme { get; private set; } = "default";
@@ -148,7 +150,7 @@ namespace PkmnLibSharp.Battling
 
         protected abstract TLearnedMove CreateLearnedMove(MoveData move, byte maxUses, MoveLearnMethod learnMethod);
 
-        public TPokemon Build()
+        public TPokemon Build(Random? random = null)
         {
             if (!Library.StaticLibrary.SpeciesLibrary.TryGet(Species, out var species))
             {
@@ -160,7 +162,10 @@ namespace PkmnLibSharp.Battling
                 throw new Exception($"Forme '{Forme}' was not found on species '{Species}'");
             }
 
-            var random = new Random();
+            if (random == null)
+            {
+                random = _defaultRandom;
+            }
 
             Item? heldItem = null;
             if (HeldItem != null)