Refactor B2WorldOverlapContext constructor to use 'in' modifier for B2ShapeProxy

- Updated `B2WorldOverlapContext` constructor to accept `B2ShapeProxy` by reference using the `in` keyword.
- This change avoids unnecessary copying of the `B2ShapeProxy` struct, improving performance.

Author: ikpil

src/Box2D.NET/B2WorldOverlapContext.cs

@@ -12,7 +12,7 @@ public struct B2WorldOverlapContext
         public B2ShapeProxy proxy;
         public object userContext;
 
-        public B2WorldOverlapContext(B2World world, b2OverlapResultFcn fcn, in B2QueryFilter filter, B2ShapeProxy proxy, object userContext)
+        public B2WorldOverlapContext(B2World world, b2OverlapResultFcn fcn, in B2QueryFilter filter, in B2ShapeProxy proxy, object userContext)
         {
             this.world = world;
             this.fcn = fcn;