Enable hostname-based proxy routing by default when proxy set

[poupas]

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[bbarao]

🤖 LLM-assisted review comment 🤖

Clean PR, two minor notes:

1. hasProxyEnv() triggers on NO_PROXY alone (root.go:229) — If only NO_PROXY is set without any actual proxy variables, hasProxyEnv() returns true and enables hostname-based routing. This allocates an IPNameCache and causes an extra DNS re-resolution per TCP connection (the IP gets translated back to a hostname, then net.Dialer resolves it again). In practice this is harmless: the second lookup uses the same system resolver, adds negligible latency, and the NO_PROXY-only scenario is unrealistic. Mentioning it for awareness, not suggesting a change.

 func hasProxyEnv() bool {
-	for _, k := range []string{"HTTP_PROXY", "http_proxy", "HTTPS_PROXY", "https_proxy", "NO_PROXY", "no_proxy"} {
+	for _, k := range []string{"HTTP_PROXY", "http_proxy", "HTTPS_PROXY", "https_proxy"} {
 		if os.Getenv(k) != "" {
 			return true
 		}
 	}
 	return false
 }

2. Stale doc example (dialers.go:48) — The TCPProxyDialer type comment still shows the old constructor signature without the new logger parameter.

-//	dialer := dialers.NewTCPProxyDialer(30 * time.Second)
+//	dialer := dialers.NewTCPProxyDialer(30 * time.Second, log)