fix(profile): request and preserve Clash subscriptions

[Crepveant]

• Request remote subscriptions using a Clash-compatible user agent.
• Retry with Clash user agent when providers return base64 protocol links or reject the default user agent.
• Preserve YAML indentation while expanding remote subscription content.
• Update hiddify-core submodule for Clash conversion support.

Depends on hiddify-core PR: hiddify/hiddify-core#129

• Imported a provider URL that returns Clash YAML with clash.meta.
• Confirmed generated config preserves YAML structure and converts through the Clash parser.
• flutter build windows