fix: drop redundant trim before split_whitespace

CI caught `clippy::trim_split_whitespace` on Rust 1.94: `split_whitespace()`
already skips leading/trailing whitespace, so `.trim()` first is redundant.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/system_dns.rs

@@ -219,7 +219,7 @@ fn discover_linux() -> SystemDnsInfo {
 #[cfg(any(target_os = "linux", test))]
 fn iter_nameservers(content: &str) -> impl Iterator<Item = &str> {
     content.lines().filter_map(|line| {
-        let mut parts = line.trim().split_whitespace();
+        let mut parts = line.split_whitespace();
         (parts.next() == Some("nameserver")).then_some(())?;
         parts.next()
     })