fix: avoid libresolv FFI for HTTPS records

[ryanfowler]

Summary

• avoid direct libresolv/res_query FFI for Linux/Unix HTTPS DNS record lookup
• use resolv.conf nameserver with the existing DNS wire/UDP/TCP path instead
• keeps normal CI and cargo-zigbuild release links from depending on resolver symbol aliases

Validation

• cargo fmt
• cargo check --locked --all-features
• cargo test --locked --all-features --lib dns::svcb::system