Adds a new `analytics` subcommand that analyzes Google Takeout mbox files
to identify top senders by message count. Designed for efficient processing
of large files (60GB+) with minimal memory usage.
Features:
- Streams files line-by-line with 1MB buffer (never loads entire file)
- Extracts sender email addresses from From: headers
- Counts messages per sender and displays top N (default 10)
- Shows progress output every 10,000 messages
- No Gmail API access needed
Usage:
cull-gmail analytics <MBOX_FILE> [-n TOP]
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
