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/classes.delivery.system.ts

@@ -1,4 +1,7 @@
 import * as plugins from '../../plugins.ts';
+import { EventEmitter } from 'node:events';
+import * as net from 'node:net';
+import * as tls from 'node:tls';
 import { logger } from '../../logger.ts';
 import { 
   SecurityLogger, 
@@ -97,7 +100,7 @@ export interface IDeliveryStats {
 /**
  * Handles delivery for all email processing modes
  */
-export class MultiModeDeliverySystem extends plugins.EventEmitter {
+export class MultiModeDeliverySystem extends EventEmitter {
   private queue: UnifiedDeliveryQueue;
   private options: Required<IMultiModeDeliveryOptions>;
   private stats: IDeliveryStats;