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/errors/index.ts

@@ -1,24 +0,0 @@
-/**
- * Error types module stub
- */
-
-export class SmtpError extends Error {
-  constructor(message: string, public code?: number) {
-    super(message);
-    this.name = 'SmtpError';
-  }
-}
-
-export class AuthenticationError extends Error {
-  constructor(message: string) {
-    super(message);
-    this.name = 'AuthenticationError';
-  }
-}
-
-export class RateLimitError extends Error {
-  constructor(message: string) {
-    super(message);
-    this.name = 'RateLimitError';
-  }
-}