Implements move execution for battle

PkmnLib.Static/Utils/EnumerableHelpers.cs

@@ -10,4 +10,27 @@ public static class EnumerableHelpers
     /// </summary>
     public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> enumerable) where T : class =>
         enumerable.Where(x => x is not null)!;
+    
+    /// <summary>
+    /// Finds the index of a value in an enumerable. Returns -1 if the value is not found.
+    /// </summary>
+    public static int IndexOf<T>(this IEnumerable<T> enumerable, T value)
+    {
+        var index = 0;
+        foreach (var item in enumerable)
+        {
+            if (item is null)
+            {
+                if (value is null)
+                    return index;
+                continue;
+            }
+            if (item.Equals(value))
+                return index;
+
+            index++;
+        }
+
+        return -1;
+    }
 }