Change use of i32 to u32 where appropriate

[Aatch]

Most of the function in the ll module take a size as an i32 type. I'm not entirely sure why I did that, as a u32 type makes more sense most of the time.

This should be a fairly simple task, just change the signatures so the size arguments are u32 instead of i32, most of them start with a debug_assert! for the size being greater than 0 anyway.