- Refactored STARTTLS implementation to use Deno's native TLS via Deno.startTls().
- Introduced ConnectionWrapper to provide a Node.js net.Socket-compatible interface for Deno.Conn and Deno.TlsConn.
- Updated TlsHandler to utilize the new STARTTLS implementation.
- Added comprehensive SMTP authentication tests for PLAIN and LOGIN mechanisms.
- Implemented rate limiting tests for SMTP server connections and commands.
- Enhanced error handling and logging throughout the STARTTLS and connection upgrade processes.