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`.

dns/transport/local/local_darwin_dhcp.go

@@ -0,0 +1,16 @@
+//go:build darwin && with_dhcp
+
+package local
+
+import (
+	"context"
+
+	"github.com/sagernet/sing-box/dns"
+	"github.com/sagernet/sing-box/dns/transport/dhcp"
+	"github.com/sagernet/sing-box/log"
+	N "github.com/sagernet/sing/common/network"
+)
+
+func newDHCPTransport(transportAdapter dns.TransportAdapter, ctx context.Context, dialer N.Dialer, logger log.ContextLogger) dhcpTransport {
+	return dhcp.NewRawTransport(transportAdapter, ctx, dialer, logger)
+}