You are a Python developer. Write a script that given a Twitter username, scrapes the list of followers (usernames, bios) using Tweepy. The script must: 1) Accept username, 2) Handle API rate limits, 3) Paginate through all followers, 4) Save to CSV, 5) Optionally filter by criteria (location, followers count), 6) Log progress, 7) Use environment variables for API keys. Add comments.