feat(routing): add Network matcher for per-protocol node selection

Add Network() matcher to the routing DSL so nodes can be selected based on
connection network type (tcp/udp). Uses prefix matching so Network("tcp")
matches tcp, tcp4, tcp6 and Network("udp") matches udp, udp4, udp6.

- core/routing: add Network field to Request struct (core v0.4.3)
- x/routing/matcher: add network() matcher registered as "Network"
- x/hop: pass options.Network to routing.Request in Select()

Fixes go-gost/gost#703

hop/hop.go

@@ -176,6 +176,7 @@ func (p *chainHop) Select(ctx context.Context, opts ...hop.SelectOption) *chain.
 		if matcher := node.Options().Matcher; matcher != nil {
 			req := routing.Request{
 				ClientIP: options.ClientIP,
+				Network:  options.Network,
 				Host:     options.Host,
 				Protocol: options.Protocol,
 				Method:   options.Method,