Support listening to a port during initialization

In theory, wizer could support a call to open a listening socket during initialization. The call would get recorded as a listening port, and when the resulting module is later loaded, the loader could listen on that port and make the resulting socket available as the same file descriptor. If the module calls `accept`, or if it checks the listening port number without first setting that port number, that would prevent initialization from progressing past that point. But otherwise, the initialization could progress past the call to `listen`, and the resulting wizened module could be used with a pre-opened socket.