src: clippy fixes

Signed-off-by: Allison Karlitskaya <allison.karlitskaya@redhat.com>

Author: allisonkarlitskaya

src/tree.rs

@@ -600,7 +600,7 @@ mod tests {
 
         dir.remove(OsStr::new("file1.txt"));
         assert_eq!(dir.entries.len(), 1);
-        assert!(dir.entries.get(OsStr::new("file1.txt")).is_none());
+        assert!(!dir.entries.contains_key(OsStr::new("file1.txt")));
 
         dir.remove(OsStr::new("nonexistent")); // Should be no-op
         assert_eq!(dir.entries.len(), 1);
@@ -635,7 +635,7 @@ mod tests {
             Some(Inode::Directory(d)) => {
                 assert_eq!(d.stat.st_mtim_sec, 90); // Stat updated
                 assert_eq!(d.entries.len(), 1); // Inner file preserved
-                assert!(d.entries.get(OsStr::new("inner_file")).is_some());
+                assert!(d.entries.contains_key(OsStr::new("inner_file")));
             }
             _ => panic!("Expected directory after merge"),
         }