Add correct sleep which works now because interrupts are re-enabled

using sti in syscalls, remove a bunch of old imports and code, move
keyboard scancode handling to keyboard.rs, add a new KeyboardEvent based
layout where press/release and unicode is handled, add a kbd_read
syscall which writes kbd events to a userspace buffer, add a usercopy
file which provides safe copying functions to userspace

kernel/src/driver/elf/loader.rs

@@ -1,6 +1,5 @@
 use core::ptr::null;
 
-use alloc::boxed::Box;
 use x86_64::structures::paging::OffsetPageTable;
 
 use crate::driver::{