feat: allow manual configuration of dns resolver

[encodeous]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for manually configuring a custom DNS resolver in Nylon. When configured, the application will use the specified DNS server (in ip:port format) for its own DNS queries instead of relying on the system's default resolver.

Key changes:

• Added DnsResolver configuration field to LocalCfg struct
• Implemented validation to ensure DNS resolver is specified in valid ip:port format
• Custom DNS resolver is set via net.DefaultResolver during Nylon initialization

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
state/config.go	Added DnsResolver string field to LocalCfg struct
state/validation.go	Added validation logic to ensure DnsResolver is a valid ip:port address using netip.ParseAddrPort
state/validation_test.go	Added test cases verifying the validation of DNS resolver values (valid IPv4:port, invalid hostname, hostname:port, and IP without port)
example/sample-node.yaml	Added documentation comment explaining the dnsresolver configuration option with example value
core/nylon.go	Implemented custom DNS resolver by configuring net.DefaultResolver with a custom dialer when DnsResolver is set

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