linters: Fix clippy issues

Latest clippy version complains about our existing code for the
following reasons:

- trait objects without an explicit `dyn` are deprecated
- `...` range patterns are deprecated
- lint `clippy::const_static_lifetime` has been renamed to
  `clippy::redundant_static_lifetimes`
- unnecessary `unsafe` block
- unneeded return statement

All these issues have been fixed through this patch, and rustfmt has
been run to cleanup potential formatting errors due to those changes.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

qcow/src/qcow.rs

@@ -1087,10 +1087,10 @@ impl QcowFile {
 
         let max_valid_cluster_offset = self.refcounts.max_valid_cluster_offset();
         if let Some(new_cluster) = self.raw_file.add_cluster_end(max_valid_cluster_offset)? {
-            return Ok(new_cluster);
+            Ok(new_cluster)
         } else {
             error!("No free clusters in get_new_cluster()");
-            return Err(std::io::Error::from_raw_os_error(ENOSPC));
+            Err(std::io::Error::from_raw_os_error(ENOSPC))
         }
     }