In some places we use the `*reinterpret_cast<const net::packed<T>*>(&x)`
pattern to reinterpret memory. This is a violation of C++'s aliasing rules,
which invokes undefined behaviour.
The blessed way to correctly reinterpret memory is to copy it into a new
object. Let's do that.
Note: the reinterpret_cast way has no performance advantage. Compilers
recognize the memory copy pattern and optimize it away.