ext4l: Add uuid() support

The filesystem uuid method is not implemented.

Add ext4l_uuid() which returns the filesystem UUID as a string and
wire it into the filesystem operations table. Add a test.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

test/py/tests/test_fs/test_ext4l.py

@@ -117,3 +117,10 @@ class TestExt4l:
             output = ubman.run_command(
                 f'ut -f fs fs_test_ext4l_read_norun fs_image={ext4_image}')
             assert 'failures: 0' in output
+
+    def test_uuid(self, ubman, ext4_image):
+        """Test that ext4l can return the filesystem UUID."""
+        with ubman.log.section('Test ext4l uuid'):
+            output = ubman.run_command(
+                f'ut -f fs fs_test_ext4l_uuid_norun fs_image={ext4_image}')
+            assert 'failures: 0' in output