Doing some further research you can make the optimized initialization of the WrappedByte vector by using it as a iterator.

  vec![0u8; len]
    .into_iter()
    .map(|x| WrappedByte(x))
    .collect::<Vec<_>>()

which will give you a list of WrappedBytes but initialized with calloc. I assume this is because llvm can see that the map is a identity function in this case and then can optimize it out.

Godbolt: https://godbolt.org/z/hxnnPcjvG