feat(storage): add mkdir to FileSystem trait with stubs

crates/servers/storage-server/src/server.rs

@@ -82,6 +82,15 @@ impl<F: FileSystem> Server for StorageServer<F> {
                     None => StorageResponse::Error,
                 }
             }
+            StorageRequest::Mkdir { path } => {
+                let buf = path.to_bytes();
+                let len = buf.iter().position(|&b| b == 0).unwrap_or(16);
+                if self.fs.mkdir(&buf[..len]) {
+                    StorageResponse::Ok
+                } else {
+                    StorageResponse::Error
+                }
+            }
         }
     }
 }