[AbstractWorkStealingScheduler] assert in runtime system in pushBottom

See merge request i4/manycore/emper!367

io: do not use IO_FORGOTTEN_FUTURES_SKIP_CQE on linux <= 5.17

See merge request i4/manycore/emper!366

Apparantly my assumption that io_uring ignores unknown cqe flags is
wrong. And io_uring < Linux 5.17 completes forgotten futures with
-EINVAL.

Fixes: e140759d

[AbstractWorkStealingScheduler] Emit warning if overflow queue is used

See merge request i4/manycore/emper!365

incorporate new io_uring features

See merge request i4/manycore/emper!364

We can not deal with cqes for forgotten Futures and not creating them
prevents the kernel and userspace overhead introduced by them.

LinuxVersion::compare reported two versions as equal if it could
find a new '.' in the first version but not in the second.
But this is clearly wrong because it skips comparision of the valid last
part.

The comparision 5.16.12 >= 5.18 returned true because compare
reported the version as equal after comparing the first parts and
finding a second '.' in the first but not the second.

Fix this behavior by marking the current position as the last but
do not skip its comparision.

Add tests for the desired behaviour.

Linux 5.18 introduces IORING_REGISTER_RING_FDS with
e7a6c00dc77aedf27a601738ea509f1caea6d673.

Registering the io_uring's fd prevents having to look it up for each
io_uring_enter call reducing contention on the process file table.
Jens Axboe reports good results in his fio based benchmarks and
I see no reason for EMPER to not register the io_uring fds, especially
because we never pass or share rings.

Do not register the global io_uring since it is shared in the SINGLE_URING
case or it is passed by the main thread to the completer thread breaking the
assumption liburing has about the registered io_uring fd.

Liburing 2.2 and Linux 5.18 support IORING_REGISTER_RING_FDS, preventing
the fget(ring_fd) overhead for each io_uring_enter call, as well as
IORING_OP_MSG_RING, greatly simplifying the IO-based sleep strategy code.

Improve terminology

See merge request i4/manycore/emper!363

To avoid confusing the fork with a heavyweight (Unix) fork(), we use
spawn/sync instead of fork/join in Fibril.

While extensibility is still a feature of EMPER, a more important
aspect is its efficiency.

Introduce EMPER_ASSERT_MSG

See merge request i4/manycore/emper!361

[log] Improve timestamp format: HHMM.SS mmmuuunnn

See merge request i4/manycore/emper!360

print blocked context FromAnywhere stats when STATS_BLOCKED_CONTEXT is set

See merge request i4/manycore/emper!359

This is analogue to what we do in emper/stats/worker.cpp since 46302a0f.

Add worker sleep stats, rework stats machinery

See merge request i4/manycore/emper!358

This further split up the stats machinery into smaller parts.

The idea of the new stats machinery is that 'stats' becomes an option
that enables the basic stats gathering infrastructure in EMPER. At
some point, it should become a non-user option, i.e., it should be
remove from meson_options.txt. Then comes a layer of fine-grained
stats control switches, which default to 'auto'. Third, a new option
called 'stats_all' is added, which, if enabled, activates all
fine-graind stats knobs that are set to 'auto'.

fix lockless io-stealing

See merge request i4/manycore/emper!357

The uninitialized continuation pointer may be returned without being
written resulting in dispatching a not valid fiber pointer.

If a CQE is stolen but no fiber is blocked on the corresponding future
IoContext::getContinuationsFromCompletions will call future->completeAndGetContinuation
which will set the future's completion but will not return a continuation.

If no continuation is returned from Future::completeAndGetContinuation
the continuation buffer is not advanced by IoContext::getContinuationsFromCompletions
(emper/io/IoContext.hpp:259).

IoContext::reapSingleCompletion does not check if a continuation was
created and assumed that continuation contains a valid Fiber* if
a CQE was successfully stolen.

Initialize continuation with nullptr, which is a valid Fiber*.

Minor changes of top-level files

See merge request i4/manycore/emper!356

Extend emper::printInfo()

See merge request !355

Add more CL Queue implementations

See merge request i4/manycore/emper!354

Work-Stealing queue fill-size stats

See merge request i4/manycore/emper!353

The calculation was previously done using integers, this lead to
MEMORY_MANAGER_VICTIM_PERCENTAGE to become 0.