style: order the __main__ demo imports as ruff wants

Stdlib before third party inside the block; the comment stays with the
dask imports it explains. Caught by the quality job, not locally.

Author: simontaurus

src/osw/utils/util.py

@@ -650,14 +650,14 @@ def wrapped_function(*args, **kwargs):
 
 # testing redirect
 if __name__ == "__main__":
+    from datetime import datetime
+    from time import sleep
+
     # Only the demo helpers below use dask; see async_parallelize for why it is
     # not imported at module scope. Needs the optional `parallel` extra.
     import dask
     from dask.diagnostics import ProgressBar
 
-    from datetime import datetime
-    from time import sleep
-
     print("Redirecting print messages to a buffer.")
     message_buffer = MessageBuffer()
     io_buffer = StringIO()