Co-authored-by: 1911860538 <[email protected]>

see #3896.

this commit ports an assortment of test cases for the client to an
in-memory socket using `tokio::io::duplex()`.

this should help reduce test flakes related to TCP close behavior.

this supersedes #3946.

Signed-off-by: katelyn martin <[email protected]>

…eturned (#3965)

The new trait method has a default implementation just returning `Instant::now()`.

An implementer can override that, such as Tokio providing support for it's pausable clock.

This refactors the way hyper handles HTTP/2 CONNECT / Extended CONNECT. Before,
an uninhabited enum was used to try to prevent sending of the `Buf` type once
the STREAM had been upgraded. However, the way it was originally written was
incorrect, and will eventually have compilation issues.

The change here is to spawn an extra task and use a channel to bridge the IO
operations of the `Upgraded` object to be `Cursor` buffers in the new task.

ref: rust-lang/rust#147588
Closes #3966 

BREAKING CHANGE: The HTTP/2 client connection no longer allows an executor
  that can not spawn itself.
  
  This was an oversight originally. The client connection will now include spawning
  a future that keeps a copy of the executor to spawn other futures. Thus, if it is
  `!Send`, it needs to spawn `!Send` futures. The likelihood of executors that match
  the previously allowed behavior should be very remote.

  There is also technically a semver break in here, which is that the
  `Http2ClientConnExec` trait no longer dyn-compatible, because it now expects to
  be `Clone`. This should not break usage of the `conn` builder, because it already
  separately had `E: Clone` bounds. If someone were using `dyn Http2ClientConnExec`,
  that will break. However, there is no purpose for doing so, and it is not usable
  otherwise, since the trait only exists to propagate bounds into hyper. Thus, the
  breakage should not affect anyone.

Revert "fix(http1): fix rare missed write wakeup on connections (#3952)"

This reverts commit 2377b89.