Finalmask: Refactor header conns to avoid multiple-copy; Add randRange to "header-custom" (TCP & UDP) (#5812)

https://github.com/XTLS/Xray-core/pull/5657#issuecomment-4016760602
https://github.com/XTLS/Xray-core/pull/5657#issuecomment-4052921628

transport/internet/finalmask/salamander/config.go

@@ -14,3 +14,6 @@ func (c *Config) WrapPacketConnClient(raw net.PacketConn, level int, levelCount
 func (c *Config) WrapPacketConnServer(raw net.PacketConn, level int, levelCount int) (net.PacketConn, error) {
 	return NewConnServer(c, raw)
 }
+
+func (c *Config) HeaderConn() {
+}