added registration for nested SyncableFields

[CoreAidan]

Added the ability for the EntityClassData constructor to find and register nested SyncableFields and their SyncVars

Since reference types are stored in the parent object as a pointer to a separately‐allocated object I've created a map that allows for chaining to the target offset.

NOTE: this is just a rough pass idea that is not final. while it does work I don't know much about optimizations. I more or less want to get your opinion as I know the multiple calls to traverse the object is a bit much I couldn't think of another way. Though as I mention it does seem to work, but was not thoroughly test.

internal struct SyncableFieldInfo
{
    public readonly string Name;

    public readonly int[] Offsets;

    public readonly SyncFlags Flags;

    public ushort RPCOffset;

    public SyncableFieldInfo(string name, int[] offsets, SyncFlags flags)
    {
        Name = name;
        Offsets = offsets;
        Flags = flags;
        RPCOffset = ushort.MaxValue;
    }
}

internal static SyncVar<T> GetSyncableSyncVar<T>(InternalBaseClass baseClass, int[] offsets) where T : unmanaged
{
    InternalBaseClass syncable = baseClass;
    for (int i = 0; i < offsets.Length-1; i++)
    {
        syncable = RefMagic.RefFieldValue<InternalBaseClass>(syncable, offsets[i]);
        if (syncable == null)
            throw new NullReferenceException($"SyncableField at offset {offsets[i]} is null");
    }
    ref var a = ref RefMagic.RefFieldValue<SyncVar<T>>(syncable, offsets[offsets.Length-1]);

    return a;
}