LibCore: Introduce SharedSingleProducerCircularQueue

This new class with an admittedly long OOP-y name provides a circular
queue in shared memory. The queue is a lock-free synchronous queue
implemented with atomics, and its implementation is significantly
simplified by only accounting for one producer (and multiple consumers).
It is intended to be used as a producer-consumer communication
datastructure across processes. The original motivation behind this
class is efficient short-period transfer of audio data in userspace.

This class includes formal proofs of several correctness properties of
the main queue operations `enqueue` and `dequeue`. These proofs are not
100% complete in their existing form as the invariants they depend on
are "handwaved". This seems fine to me right now, as any proof is better
than no proof :^). Anyways, the proofs should build confidence that the
implemented algorithms, which are only roughly based on existing work,
operate correctly in even the worst-case concurrency scenarios.

Meta/CMake/all_the_debug_macros.cmake

@@ -164,6 +164,7 @@ set(SERVICE_DEBUG ON)
 set(SH_DEBUG ON)
 set(SHELL_JOB_DEBUG ON)
 set(SH_LANGUAGE_SERVER_DEBUG ON)
+set(SHARED_QUEUE_DEBUG ON)
 set(SIGNAL_DEBUG ON)
 set(SLAVEPTY_DEBUG ON)
 set(SMP_DEBUG ON)