Various I/O operations need to have optional timeouts

[brson]

Right now you just get whatever timeout the underlying OS decides to give you, and apparently it's very long (or maybe infinite). This is especially a problem for connect methods, where there's no object that can be forcibly closed from other threads.

• TCP/unix connect std: Add timeouts to unix connect/accept #13723, std: Add an experimental connect_timeout function #13604
• TCP/udp/unix read/write Read/write I/O timeouts #13814
• TCP/unix accept std: Add support for an accept() timeout #13688,
• Process wait io: Implement process wait timeouts #13957