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

test/suite/smtpclient_rfc-compliance/test.crfc-02.esmtp-compliance.ts

@@ -74,4 +74,4 @@ tap.test('CRFC-02: Basic ESMTP Compliance', async () => {
   }
 });
 
-tap.start();
+export default tap.start();

test/suite/smtpclient_rfc-compliance/test.crfc-03.command-syntax.ts

@@ -64,4 +64,4 @@ tap.test('CRFC-03: SMTP Command Syntax Compliance', async () => {
   }
 });
 
-tap.start();
+export default tap.start();

test/suite/smtpclient_rfc-compliance/test.crfc-04.response-codes.ts

@@ -51,4 +51,4 @@ tap.test('CRFC-04: SMTP Response Code Handling', async () => {
   }
 });
 
-tap.start();
+export default tap.start();

test/suite/smtpclient_rfc-compliance/test.crfc-05.state-machine.ts

@@ -700,4 +700,4 @@ tap.test('CRFC-05: should comply with SMTP state machine (RFC 5321)', async (too
   console.log(`\n${testId}: All ${scenarioCount} state machine scenarios tested ✓`);
 });
 
-tap.start();
+export default tap.start();

test/suite/smtpclient_rfc-compliance/test.crfc-06.protocol-negotiation.ts

@@ -685,4 +685,4 @@ tap.test('CRFC-06: should handle protocol negotiation correctly (RFC 5321)', asy
   console.log(`\n${testId}: All ${scenarioCount} protocol negotiation scenarios tested ✓`);
 });
 
-tap.start();
+export default tap.start();

test/suite/smtpclient_rfc-compliance/test.crfc-07.interoperability.ts

@@ -725,4 +725,4 @@ tap.test('CRFC-07: should ensure SMTP interoperability (RFC 5321)', async (tools
   console.log(`\n${testId}: All ${scenarioCount} interoperability scenarios tested ✓`);
 });
 
-tap.start();
+export default tap.start();