Improve local DNS server on darwin

We mistakenly believed that `libresolv`'s `search` function worked correctly in NetworkExtension, but it seems only `getaddrinfo` does.

This commit changes the behavior of the `local` DNS server in NetworkExtension to prefer DHCP, falling back to `getaddrinfo` if DHCP servers are unavailable.

It's worth noting that `prefer_go` does not disable DHCP since it respects Dial Fields, but `getaddrinfo` does the opposite. The new behavior only applies to NetworkExtension, not to all scenarios (primarily command-line binaries) as it did previously.

In addition, this commit also improves the DHCP DNS server to use the same robust query logic as `local`.

option/dns.go

@@ -190,7 +190,7 @@ func (o *DNSServerOptions) Upgrade(ctx context.Context) error {
 		}
 	}
 	remoteOptions := RemoteDNSServerOptions{
-		LocalDNSServerOptions: LocalDNSServerOptions{
+		RawLocalDNSServerOptions: RawLocalDNSServerOptions{
 			DialerOptions: DialerOptions{
 				Detour: options.Detour,
 				DomainResolver: &DomainResolveOptions{
@@ -211,7 +211,7 @@ func (o *DNSServerOptions) Upgrade(ctx context.Context) error {
 	switch serverType {
 	case C.DNSTypeLocal:
 		o.Type = C.DNSTypeLocal
-		o.Options = &remoteOptions.LocalDNSServerOptions
+		o.Options = &remoteOptions.RawLocalDNSServerOptions
 	case C.DNSTypeUDP:
 		o.Type = C.DNSTypeUDP
 		o.Options = &remoteOptions
@@ -363,7 +363,7 @@ type HostsDNSServerOptions struct {
 	Predefined *badjson.TypedMap[string, badoption.Listable[netip.Addr]] `json:"predefined,omitempty"`
 }
 
-type LocalDNSServerOptions struct {
+type RawLocalDNSServerOptions struct {
 	DialerOptions
 	Legacy              bool           `json:"-"`
 	LegacyStrategy      DomainStrategy `json:"-"`
@@ -371,8 +371,13 @@ type LocalDNSServerOptions struct {
 	LegacyClientSubnet  netip.Prefix   `json:"-"`
 }
 
+type LocalDNSServerOptions struct {
+	RawLocalDNSServerOptions
+	PreferGo bool `json:"prefer_go,omitempty"`
+}
+
 type RemoteDNSServerOptions struct {
-	LocalDNSServerOptions
+	RawLocalDNSServerOptions
 	DNSServerAddressOptions
 	LegacyAddressResolver      string             `json:"-"`
 	LegacyAddressStrategy      DomainStrategy     `json:"-"`