feat: prefer secure connections in server discovery fallback

[dongfengweixiao]

When discovering mail server settings, prefer secure (TLS) connections over non-secure ones for IMAP, POP, and SMTP protocols. Previously the code selected the first ready connection regardless of security status, which could result in preferring a plaintext connection even when a secure alternative was available.

bug log:

┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
│ #0   AppLifecycle.build (package:enough_mail_app/src/app_lifecycle/provider.dart:40:12)
│ #1   NotifierProviderImpl.runNotifierBuild (package:riverpod/src/notifier/base.dart:166:38)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 emitting non-ignored state: AppLifecycleState.resumed
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
discover settings for user@example.com
Discover: trying https://autoconfig.example.com/mail/config-v1.1.xml?emailaddress=user@example.com
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
│ #0   EnoughMailApp.build.<anonymous closure> (package:enough_mail_app/src/app.dart:49:14)
│ #1   __AppLifecycleStateState.didChangeAppLifecycleState (package:flutter_hooks/src/widgets_binding_observer.dart:59:26)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 raw AppLifecycleState changed from AppLifecycleState.resumed to AppLifecycleState.inactive
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
│ #0   AppLifecycle.build (package:enough_mail_app/src/app_lifecycle/provider.dart:40:12)
│ #1   NotifierProviderImpl.runNotifierBuild (package:riverpod/src/notifier/base.dart:166:38)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 emitting non-ignored state: AppLifecycleState.inactive
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Discover: trying http://autoconfig.example.com/mail/config-v1.1.xml?emailaddress=user@example.com
mxDomain for [example.com] is [example.org]
Discover: trying https://autoconfig.example.org/mail/config-v1.1.xml?emailaddress=user@example.com
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
│ #0   EnoughMailApp.build.<anonymous closure> (package:enough_mail_app/src/app.dart:49:14)
│ #1   __AppLifecycleStateState.didChangeAppLifecycleState (package:flutter_hooks/src/widgets_binding_observer.dart:59:26)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 raw AppLifecycleState changed from AppLifecycleState.inactive to AppLifecycleState.resumed
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
│ #0   AppLifecycle.build (package:enough_mail_app/src/app_lifecycle/provider.dart:40:12)
│ #1   NotifierProviderImpl.runNotifierBuild (package:riverpod/src/notifier/base.dart:166:38)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 emitting non-ignored state: AppLifecycleState.resumed
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Discover: trying http://autoconfig.example.org/mail/config-v1.1.xml?emailaddress=user@example.com
Discover: trying https://autoconfig.thunderbird.net/v1.1/example.com
Discover: trying https://autoconfig.thunderbird.net/v1.1/example.org
success at mail.example.org:143
success at mail.example.org:110
success at mail.example.com:110
success at mail.example.com:143
failed at imap.example.com:993
failed at imap.example.com:143
failed at imap.example.com:995
failed at imap.example.com:110
success at pop.example.org:143
success at pop.example.org:110
success at smtp.example.org:587
success at smtp.example.org:25
failed at out.example.com:465
failed at out.example.com:587
failed at out.example.com:25
failed at imap.example.org:993
failed at imap.example.org:143
failed at imap.example.org:995
failed at imap.example.org:110
failed at out.example.org:465
failed at out.example.org:587
failed at out.example.org:25
failed at mail.example.com:993
failed at pop.example.org:995
failed at smtp.example.org:465
success at mail.example.org:993
failed at mail.example.com:995
failed at pop.example.org:993
success at mail.example.org:995
failed at in.example.com:993
failed at in.example.com:143
failed at in.example.com:995
failed at in.example.com:110
failed at pop.example.com:993
failed at pop.example.com:143
failed at pop.example.com:995
failed at pop.example.com:110
failed at smtp.example.com:465
failed at smtp.example.com:587
failed at smtp.example.com:25
failed at in.example.org:993
failed at in.example.org:143
failed at in.example.org:995
failed at in.example.org:110

found mail server for example.com:
incoming: mail.example.com:143 (ServerType.imap)
outgoing: smtp.example.org:587 (ServerType.smtp)
done discovering settings: example.com