Merge #212

212: 'copy_from_slice' instead of 'clone_from_slice' when copying 'u8' slices r=JOE1994 a=JOE1994

Hello :crab: ,
this PR changes invocations of `clone_from_slice()` to `copy_from_slice()`.
`copy_from_slice()` performs memcpy, while `clone_from_slice()` performs an element-wise copy.
(`copy_from_slice()` should generally run faster than `clone_from_slice()`)

The affected call sites all copy `u8` slices, and since `u8` implements `Copy`, it is safe to use `copy_from_slice()`.

Thank you for reviewing this PR :superhero_woman: :superhero_man: :superhero: 

Co-authored-by: JOE1994 <joseph942010@gmail.com>