Fix overflow panic when using `Duration::MAX` for timeout

I tried to get away with passing `Duration::MAX` as a timeout to a function that ultimately called `Receiver::recv_timeout`, and got a panic. [The docs](https://doc.rust-lang.org/stable/std/time/struct.Instant.html#os-specific-behaviors) say > For cross-platform code, you can comfortably use durations of up to around one hundred years. This PR avoids the panic by approximating durations over 100 years (or however far away your platform's maximum `Instant` is) with "never".