Stream new Gmail messages as NDJSON with Pub/Sub-backed polling and optional file output.

• Monitors incoming emails via Gmail API with configurable label filtering (INBOX, UNREAD, etc.) and message format options (full, metadata, minimal, raw)
• Supports two setup modes: automatic Pub/Sub topic and subscription creation, or connection to existing resources
• Configurable polling interval, batch size, and one-time pull mode; graceful shutdown with optional resource cleanup
• Can write each message to a separate JSON file or stream directly to stdout; watch sessions expire after 7 days and must be renewed