Don't assume u32 alignment of random() state buffer

This MR addresses the issue of using u32-based algorithms on a possibly user-supplied (char *) state buffer that is not required to be u32-aligned. This means lots of to_ne_bytes() and from_ne_bytes(), but that seems to be the price to pay for avoiding UB.

Another fix included here is the use of a proper wrapping_add() instead of a possibly panicking += in the random() function.