feature: cleaning up the API to accommodate .net 8 Numerics compatibility.

src/DotRecast.Core/Numerics/RcVec2f.cs

@@ -16,18 +16,6 @@ namespace DotRecast.Core.Numerics
             Y = y;
         }
 
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public float Get(int idx)
-        {
-            if (0 == idx)
-                return X;
-
-            if (1 == idx)
-                return Y;
-
-            throw new IndexOutOfRangeException("vector2f index out of range");
-        }
-
         public override bool Equals(object obj)
         {
             if (!(obj is RcVec2f))

src/DotRecast.Core/Numerics/RcVecExtensions.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Runtime.CompilerServices;
+using DotRecast.Core.Numerics;
+
+namespace DotRecast.Core.Numerics
+{
+    public static class RcVecExtensions
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float Get(this RcVec2f v, int i)
+        {
+            switch (i)
+            {
+                case 0: return v.X;
+                case 1: return v.Y;
+                default: throw new IndexOutOfRangeException("vector2f index out of range");
+            }
+        }
+    }
+}