synqueue

This is an experimental queue to be used in multi-threaded scenarios, like the task processors. More specifically:

• internally synchronized for both consumers and producers (MPMC).
• backed by an array, which is fast to access
• bounded: the capacity is specified at creation

Unlike other implementations, such as crossbeam-queue, it doesn't carry a atomic bit per element.
Checked by both Miri and Loom on CI.

Note: experimental and currently slower than alternatives.