figure out how to work with temporal streams too

[yoshuawuyts]

[yoshuawuyts]

We need to distinguish between a deadline and a boundary. Deadlines are hit exactly once. Boundaries can be hit multiple times.

[yoshuawuyts]

Maybe we should rename {AsyncIter, Future}::until with:

• AsyncIter::timeout takes impl Boundary
• AsyncIter::timeout_at takes impl Deadline
• Future:timeout takes impl Boundary
• Future::timeout_at takes impl Deadline

note: timeout_at takes StopToken, Instant, and possibly SystemTime.

[yoshuawuyts]

Prior art for this naming:

• https://www.learnrxjs.io/learn-rxjs/operators/utility/timeout
• https://docs.rs/tokio/latest/tokio/time/index.html#functions