It is tempting to use very large `Duration` value to get a practically
infinite timeout.
Before this commit Tokio panics on checked Instant + Duration
overflow.
This commit implements very simple fix: if Instant + Duration
overflows, we use duration = 30 years. Better fix should avoid
firing a timer on duration overflow. It requires deeper understanding
how timers work, but also it is not clear, for example, what
`Sleep::deadline` function should return.
Similar fix is done for `sleep`.
Before this commit `close` after successful `try_recv` panics.
My use case is this: on drop, I call `close` to prevent pushing a
message to the queue, and then fetch the message if any and process
it.
But if message is already processed, `close` panics. And there is
no API to know if message was already fetched or not (except for
writing a wrapped which would track that info, which would be an
overkill).
But generally `close` operation should be safe to be called any
time.
