Add a Table::zero method to clear all entries

src/memory/paging/table.rs

@@ -6,6 +6,14 @@ pub struct Table {
     entries: [Entry; ENTRY_COUNT],
 }
 
+impl Table {
+    pub fn zero(&mut self) {
+        for entry in self.entries.iter_mut() {
+            entry.set_unused();
+        }
+    }
+}
+
 impl Index<usize> for Table {
     type Output = Entry;