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As part of debugging full-route tunneling on Windows, we discovered that we need to always explicitly choose the interface through which we want to send packets, otherwise Windows may cause a routing loop by routing our packets back into the TUN device. We already have a `SocketFactory` abstraction in `connlib` that is used by each platform to customise the setup of each socket to prevent routing loops. So far, this abstraction directly returns tokio sockets which don't allow us to intercept the actual sending of packets. For some of our traffic, i.e. the UDP packets exchanged with relays, we don't specify a source address. To make full-route work on Windows, we need to intercept these packets and explicitly set the source address. To achieve that, we introduce dedicated `TcpSocket` and `UdpSocket` structs within `socket-factory`. With this in place, we will be able to add Windows-conditional code to looks up and sets the source address of outgoing UDP packets. For TCP sockets, the lookup will happen prior to connecting to the address and used to bind to the correct interface. Related: #2667. Related: #5955.