feat: Implement Deno-native STARTTLS handler and connection wrapper

- 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.

ts/mail/delivery/smtpserver/interfaces.ts

@@ -476,11 +476,16 @@ export interface ISmtpServerOptions {
      * Whether authentication is required
      */
     required: boolean;
-    
+
     /**
      * Allowed authentication methods
      */
     methods: ('PLAIN' | 'LOGIN' | 'OAUTH2')[];
+
+    /**
+     * Whether TLS is required for authentication (default: true)
+     */
+    requireTLS?: boolean;
   };
   
   /**