feat!: Remove until & remove option from accept

[tmccombs]

Accepting a connection in all cases that I am aware of is an operation that either succeeds or gives an error. It doesn't really make sense for it to return an Option<Result<...>>. Changing the return type to just Result<..> simplifies not only this library, but also any additional implementations of AsyncAccept and any usages of TlsListener.accept().

The one use case, where we needed an Option was if the AsyncAccept trait was configured to end when another future finished first. However, this functionality is already (mostly) available with the StreamExt::take_until method.

I will note that the behavior with take_until is slightly different. With the previous Until impementation, if a tcp connection had been successfully established, but the TLS handshake hadn't been established yet, when the finalization future completed, then we would continue processing that connection.

However, with StreamExt::take_until, such
a connection would be dropped, since it checks the finalizaition future before polling the stream. I hope that in the vast majority of cases this doesn't really matter, or is a better behavior.

BREAKING CHANGE: remove until from AsyncAccept trait. Use
StreamExt.take_until on the TlsListener instead.
BREAKING CHANGE: accept fn on AsyncAccept trait no longer returns an
Option
BREAKING CHANGE: accept fn on TlsListener no longer returns an Option