import: fix broken progressbar when importing folder

Add child progress bar to dvc fs to report directory import progress correctly.

Fixes #10677

Author: pchmelaratinno

dvc/fs/dvc.py

@@ -578,7 +578,10 @@ def get_file(arg: tuple[FileSystem, tuple[str, str, Optional[dict]]]):
             kw = kwargs
             if isinstance(fs, DataFileSystem):
                 kw = kw | {"info": info}
-            return fs.get_file(src, dest, callback=callback, **kw)
+            with callback.branched(src, dest) as child:
+                file = fs.get_file(src, dest, callback=child, **kw)
+            callback.relative_update()
+            return file
 
         if batch_size == 1:
             ctx: AbstractContextManager = nullcontext()