fix(smtp): improve port handling and response parsing; enhance DKIM signing process

- Updated port assignment logic to handle undefined values correctly.
- Refactored SMTP response parsing to better handle multi-line responses.
- Improved DKIM signing by canonicalizing headers and body, ensuring correct header order.
- Added checks for expected SMTP response codes.
- Enhanced error handling during DKIM signing.
- Adjusted the way additional headers are inserted into the MIME message.

test: skip mailCrab integration tests in non-GitHub Actions environments

Author: productdevbook

package.json

@@ -3,7 +3,7 @@
   "type": "module",
   "version": "0.1.0",
   "private": false,
-  "packageManager": "pnpm@10.8.1",
+  "packageManager": "pnpm@10.10.0",
   "description": "A modern TypeScript email library with zero dependencies, supporting multiple providers including AWS SES, Resend, MailCrab, and HTTP APIs",
   "author": "productdevbook <[email protected]>",
   "license": "MIT",
@@ -96,16 +96,16 @@
   },
   "devDependencies": {
     "@antfu/eslint-config": "^4.12.0",
-    "@types/node": "^22.14.1",
-    "@vitest/coverage-v8": "^3.1.1",
+    "@types/node": "^22.15.3",
+    "@vitest/coverage-v8": "^3.1.2",
     "bumpp": "^10.1.0",
     "dotenv": "^16.5.0",
-    "eslint": "^9.24.0",
+    "eslint": "^9.26.0",
     "ts-node": "^10.9.2",
     "typescript": "^5.8.3",
     "unbuild": "^3.5.0",
     "vite-tsconfig-paths": "^5.1.4",
-    "vitest": "^3.1.1"
+    "vitest": "^3.1.2"
   },
   "resolutions": {
     "unemail": "link:."