Update tower-batch to avoid hangs on drop

[teor2345]

Is your feature request related to a problem? Please describe.

tower-batch is missing a semaphore fix that wakes waiting clones on close: tower-rs/tower#480

Describe the solution you'd like

• Copy the version of semaphore.rs included in our pinned version of tower, to tower-batch/src/: https://github.com/tower-rs/tower/blob/d4d1c67c6a0e4213a52abcc2b9df6cc58276ee39/tower/src/semaphore.rs
• Add the Sync bound to the semaphore future
• Update tower_batch::Buffer: https://github.com/tower-rs/tower/pull/480/files#diff-35398bbf39b455b121231a971e231cfc669556eda1c98705f367aa774f3da86c
  • use new_with_close in pair
  • use pair in new
• Update tower_batch::Worker: https://github.com/tower-rs/tower/pull/480/files#diff-868107348117bb575baa89a1a3aae31fb03e020ed6d709fe45443c4d65aefceb
  • use pin_project(PinnedDrop) on Worker
  • add close to Worker
  • use close to wake waiting tasks on error
  • copy PinnedDrop

Describe alternatives you've considered

Do nothing: tower-buffer users might hang.

Additional context

This issue was discovered during the review in #1593. It was partly fixed by #1671.

[mpguerra]

closed by #1908