Enable splice for freedom outbound (downlink only)

- Add outbound name
- Add outbound conn in ctx
- Refactor splice: it can be turn on from all inbounds and outbounds
- Refactor splice: Add splice copy to vless inbound
- Fix http error test
- Add freedom splice toggle via env var
- Populate outbound obj in context
- Use CanSpliceCopy to mark a connection
- Turn off splice by default

proxy/shadowsocks_2022/inbound.go

@@ -66,6 +66,7 @@ func (i *Inbound) Network() []net.Network {
 func (i *Inbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022"
+	inbound.SetCanSpliceCopy(3)
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/inbound_multi.go

@@ -155,6 +155,7 @@ func (i *MultiUserInbound) Network() []net.Network {
 func (i *MultiUserInbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022-multi"
+	inbound.SetCanSpliceCopy(3)
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/inbound_relay.go

@@ -87,6 +87,7 @@ func (i *RelayInbound) Network() []net.Network {
 func (i *RelayInbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022-relay"
+	inbound.SetCanSpliceCopy(3)
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/outbound.go

@@ -66,12 +66,14 @@ func (o *Outbound) Process(ctx context.Context, link *transport.Link, dialer int
 	inbound := session.InboundFromContext(ctx)
 	if inbound != nil {
 		inboundConn = inbound.Conn
+		inbound.SetCanSpliceCopy(3)
 	}
 
 	outbound := session.OutboundFromContext(ctx)
 	if outbound == nil || !outbound.Target.IsValid() {
 		return newError("target not specified")
 	}
+	outbound.Name = "shadowsocks-2022"
 	destination := outbound.Target
 	network := destination.Network