Add drop to safely deallocate memory

cache_utils/src/mmap.rs

@@ -1,5 +1,6 @@
 #![cfg(feature = "std")]
 
+use core::ffi::c_void;
 use core::ptr::null_mut;
 use core::slice::{from_raw_parts, from_raw_parts_mut};
 use nix::sys::mman;
@@ -43,3 +44,11 @@ impl MMappedMemory {
         unsafe { from_raw_parts_mut(self.pointer, self.size) }
     }
 }
+
+impl Drop for MMappedMemory {
+    fn drop(&mut self) {
+        unsafe {
+            mman::munmap(self.pointer as *mut c_void, self.size).unwrap();
+        }
+    }
+}