TransformExtensionMethods.cs

using UnityEngine;

namespace Kogane
{
    public static class TransformExtensionMethods
    {
        public static Vector3 TransformPointUnscaled
        (
            this Transform self,
            in   Vector3   position
        )
        {
            var localToWorldMatrix = Matrix4x4.TRS
            (
                pos: self.position,
                q: self.rotation,
                s: Vector3.one
            );

            return localToWorldMatrix.MultiplyPoint3x4( position );
        }

        public static Vector3 InverseTransformPointUnscaled
        (
            this Transform self,
            in   Vector3   position
        )
        {
            var worldToLocalMatrix = Matrix4x4.TRS
            (
                pos: self.position,
                q: self.rotation,
                s: Vector3.one
            ).inverse;

            return worldToLocalMatrix.MultiplyPoint3x4( position );
        }
    }
}