fix(mail): migrate filesystem helpers to fsUtils, update DKIM and mail APIs, harden SMTP client, and bump dependencies

test/test.smartmail.ts

@@ -158,7 +158,9 @@ tap.test('Email and Smartmail compatibility - should convert between formats', a
   // Add recipient and attachment
   smartmail.addRecipient('recipient@example.com');
   
-  const attachment = await plugins.smartfile.SmartFile.fromString(
+  // Use SmartFileFactory for creating SmartFile instances (smartfile v13+)
+  const smartFileFactory = plugins.smartfile.SmartFileFactory.nodeFs();
+  const attachment = smartFileFactory.fromString(
     'test.txt',
     'This is a test attachment',
     'utf8',