Support building with #![deny(unsafe_op_in_unsafe_fn)]

As described in RFC 2585, the future direction of Rust involves requiring unsafe blocks also in unsafe functions, beginning with a warning in Rust 2024. The unsafe blocks help contain the unsafety needed, see the RFC for further details.

I just tried a quick build with #![deny(unsafe_op_in_unsafe_fn)]. As of this writing, this causes 2406 errors when building.