ByteOrder not respected across Structured boundaries

[lojack5]

This one's a difficult one:

class Inner(Structured, byte_order=ByteOrder.LE):
  val: uint32

class Outer(Structured, byte_order=ByteOrder.BE):
  inner: Inner

Here when Outer is unpacked, its inner attribute still unpacks with Little-Endian byte order. We'll have to be careful about how we solve this, since the StructuredSerializer delegates to the Inner class itself, so we can't do a simple Inner.serializer.with_byte_order, otherwise we modify the class in place.