rust: functions that reference raw pointers are unsafe

rust: functions that reference raw pointers are unsafe

Based on the Rust clippy lint that recommends that any public
function that dereferences a raw pointer, mark all FFI functions
that reference raw pointers with build_slice and cast_pointer
as unsafe.

This commits starts by removing the unsafe wrapper inside
the build_slice and cast_pointer macros then marks all
functions that use these macros as unsafe.

Then fix all not_unsafe_ptr_arg_deref warnings from clippy.

Fixes clippy lint:
https://rust-lang.github.io/rust-clippy/master/index.html#not_unsafe_ptr_arg_deref