feat(storage): add comprehensive tests for StorageManager with memory, filesystem, and custom function backends

feat(email): implement EmailSendJob class for robust email delivery with retry logic and MX record resolution

feat(mail): restructure mail module exports for simplified access to core and delivery functionalities

ts/mail/delivery/smtpclient/command-handler.ts

@@ -3,7 +3,7 @@
  * SMTP command sending and response parsing
  */
 
-import * as plugins from '../../../plugins.ts';
+import { EventEmitter } from 'node:events';
 import { SMTP_COMMANDS, SMTP_CODES, LINE_ENDINGS } from './constants.ts';
 import type { 
   ISmtpConnection, 
@@ -19,7 +19,7 @@ import {
 } from './utils/helpers.ts';
 import { logCommand, logDebug } from './utils/logging.ts';
 
-export class CommandHandler extends plugins.EventEmitter {
+export class CommandHandler extends EventEmitter {
   private options: ISmtpClientOptions;
   private responseBuffer: string = '';
   private pendingCommand: { resolve: Function; reject: Function; command: string } | null = null;