Revert "Remove throttling code"

This reverts commit 78074db.

Author: bhrutledge

twine/repository.py

@@ -184,14 +184,15 @@ def _upload(self, package: package_file.PackageFile) -> requests.Response:
                 rich.progress.TransferSpeedColumn(),
                 disable=self.disable_progress_bar,
             ) as progress:
-                task_id = progress.add_task("", total=encoder.len)
+                task_id = progress.add_task("Progress:", total=encoder.len)
+
+                def update_progress(monitor):  # type: ignore
+                    progress.update(task_id, completed=monitor.bytes_read)
+                    import time; time.sleep(0.2)  # fmt: skip
 
                 monitor = requests_toolbelt.MultipartEncoderMonitor(
                     encoder,
-                    lambda monitor: progress.update(
-                        task_id,
-                        completed=monitor.bytes_read,
-                    ),
+                    update_progress,
                 )
 
                 resp = self.session.post(