block: qcow: Implement Deref for VecCache

Add Deref<Target = [T]> implementation for VecCache<T> to allow direct
slice operations without explicitly calling get_values(). This enables
cleaner code patterns like cache.iter() instead
of cache.get_values().iter().

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/qcow/vec_cache.rs

@@ -7,7 +7,7 @@
 use std::collections::HashMap;
 use std::collections::hash_map::IterMut;
 use std::io;
-use std::ops::{Index, IndexMut};
+use std::ops::{Deref, Index, IndexMut};
 use std::slice::SliceIndex;
 
 /// Trait that allows for checking if an implementor is dirty. Useful for types that are cached so
@@ -85,6 +85,14 @@ impl<T: 'static + Copy + Default> IndexMut<usize> for VecCache<T> {
     }
 }
 
+impl<T: 'static + Copy + Default> Deref for VecCache<T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        &self.vec
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct CacheMap<T: Cacheable> {
     capacity: usize,