Don't derive Copy/Clone for Frame so we can be sure that it's free

If a Frame would be clonable or even Copy, the frame could be freed (e.g. passed to deallocate_frame) and used thereafter. Or it could be freed multiple times.

src/memory/mod.rs

@@ -4,7 +4,7 @@ mod area_frame_allocator;
 
 pub const PAGE_SIZE: usize = 4096;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Frame {
     number: usize,
 }