ApiNetworkStruct.cs

namespace ApiNetworkStruct
{
    public struct A { }
    public struct B { }
    public struct C { }
}

// en use you class
using ApiNetworkStruct;

// version 2

public static class ApiNetworkStruct
{
    public struct A { }
    public struct B { }
    public struct C { }
}

// en use you class
using static ApiNetworkStruct;