Fix high CPU usage of idle workers

[adzialocha]

This uses deadqueue, a FIFO-queue implementation wrapping crossbeam_queue::SegQueue. It extends it with a future on pop which uses a nice semaphore logic internally allowing us to await on it. This gives us exactly what we need to not naively unblock the async task and retry the queue manually on every loop cycle, as there was otherwise no future to wait for before. This led originally to unnecessary waking of the runtime even when there was nothing to do, wasting CPU resources. With the new await / future on the queue we have a chance now to do something else in the async runtime and come back as soon as there is something to do again.

Closes: #127

📋 Checklist

• Add tests that cover your changes
• Add this PR to the Unreleased section in CHANGELOG.md
• Link this PR to any issues it closes
• New files contain a SPDX license header

[adzialocha]

Doggo not working so hard anymore 🥲

[sandreae]

Looks like a very neat solution 👍 and thanks for tidying up the PR hash prefixes ;-p