Improve documentation in progressbar module

Author: openhands-agent

progressbar/bar.py

@@ -1,3 +1,10 @@
+"""
+This module provides core classes and mixins for rendering progress bars.
+
+It includes the main `ProgressBar` class and mixins for handling file descriptors,
+resizing, and standard output redirection. It also defines base classes for progress
+bar implementations and utility functions for formatting the progress bar display.
+"""
 from __future__ import annotations
 
 import abc