feat(dns): add edns subnet config

[ibigbug]

🤔 This is a ...

• New feature
• Bug fix
• Performance optimization
• Enhancement feature
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Workflow
• Other (about what?)

🔗 Related issue link

close #938

💡 Background and solution

Implements EDNS Client Subnet support for DNS queries to provide geolocation hints to upstream DNS servers.

Problem: DNS queries don't include client subnet information, which can result in suboptimal CDN routing and slower response times.

Solution:

• Added edns-client-subnet configuration option in DNS settings
• Supports both IPv4 and IPv6 subnet configuration
• Automatically applies appropriate subnet based on query type (prefers IPv6 for AAAA queries)
• Respects existing EDNS Client Subnet options in queries

Configuration example:

dns:
  edns-client-subnet:
    ipv4: 1.2.3.0/24
    ipv6: 2001:db8::/56

📝 Changelog

• New feature: Added EDNS Client Subnet support for DNS queries
• Configuration: New edns-client-subnet option with ipv4 and ipv6 fields
• Behavior: Automatically includes client subnet information in upstream DNS queries when configured

☑️ Self-Check before Merge

• Doc is updated/provided or not needed
• Changelog is provided or not needed

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