The SpuriousFutex2Semaphore is able to notify a specific worker
by using two futexes two wait on.

One working like a normal semaphore used for global non specific
notifications via notify() and notify_many().

And a second one per worker which is based on a SleeperState.
To notify a specific worker we change its SleeperState to Notified
and call FUTEX_WAKE if needed.

The FiberHint is needed to decide in the runtime which worker to wake up.
* Hint(Worker, FiberSource::inbox) -> try to notify the specific worker
* Hint(FiberSource::{local,anywhereQueue}) -> notify anyone

The first case is needed because due to the new worker local inbox queues
we must notify the worker of the queue to prevent sleep locks.
The SemaphoreSleepStrategy already has a notifySpecific implementation
but it is very naive badly and we should implement new ones.

The second case is the what the runtime has done before.
Its WakeupStrategy decides how many workers the SleepStrategy should
wake up.

Also remove default CallerEnvironment template parameters to prevent
errors where the CallerEnvironment was forgotten and not passed on a
call side.

The new class is used when specific location of a Fiber is needed
it combines a emper::FiberSource with an workerid_t.
This replaces the hints using TaggedPtrs with IoContext::PointerTags.

IoContext::PointerTags::NewWork{Wsq,Aq} becomes
IoContext::PointerTags::NewWorkNotification.

This function is needed to deal with worker local ressources: io_uring
requests for example.

Each worker now always has a MPSC inbox queue which was already used
in the laws scheduling strategy.
Fibers can be scheduled to a specific worker using the new
Scheduler::scheduleOn method.

Since the inbox queues are now always present we can use a single
FiberSource enum combining AbstractWorkStealingStrategy::FiberSource
and LawsStrategy::FiberSource.

The laws strategy now uses the inbox queues as its priority queues.
With the only differenze that when scheduling to a inbox queue
using the Scheduler::scheduleOn the Fiber lifes only in the inbox
queue and not also simultaneously in a WSQ.

Unrelated code changes made while touching the code anyway:
* Introduce FiberSource::io which hints that a Fiber comes from the
  worker's own CQ.
* Strongly type the fiber's source in NextFiberResult.
* Make all scheduler functions return std::optional<NextFiberResult>
* Cleanup the identation in nextFiberResultViaWorkStealing

Improve log messages

See merge request !311

We commonly use foo=0x1234 in log messages in EMPER.

Log tags should not be longer than 5 characters.

[log] Use system_clock instead of high_resolution_clock

See merge request !309

[TimeoutTest] fix timeout return assertion for linux 5.16

See merge request !310

I could not identify the commit that changes this behavior but
it is reproducible on our bigboxes and my arch system.

According to the 'Notes' section of
https://en.cppreference.com/w/cpp/chrono/high_resolution_clock one
should just use steady_clock or system_clock. Furthermore, the notes
state that with GCC's libstdc++ high_resolution_clock is system_clock,
but for LLVM's libc++ it depends on the configuration (and is
steady_clock). But steady_clock has no to_time_t() member function.

Hence we explicitly uses system_clock now, which always has
to_time_t(), i.e. in libstdc++ and in libc++. This allows us to get
rid of the GLIBCXX (libstdc++) specific code.

Optionally build with libc++

See merge request !307

[meson] Add use_bundled_deps option

See merge request !308

[PipeSleepStrategy] Fix memory_order of atomic.store()

See merge request !306

The memory order of stores must be one of relaxed, release, or
seq_cst. Using 'acquire' with a store is, not allowed.

[IoContext] fix types when tracking request in flight

See merge request !304

The count used to track the requests is unsigned and negating it before
using it as long does not what we want.

Fixes: 799e5055

[UnblockOnMainActorTest] adjust workload to log level

See merge request !303

The UnblockOnMainActorTest regularly timeout in our CI
which looks to be a regular timeout because I could easily reproduce
the timeout on fauibig03.

Hopefully this change fixes regular timeouts like
https://gitlab.cs.fau.de/aj46ezos/emper/-/jobs/506757
in the CI and only leaves real faulty timeouts.

[meson] add boost as dependency

See merge request !301

I setup a new development environment and emper did not compile because
emper::io::Stats use the circular_buffer provided by boost.
Boost was not installed and our build-system failed to detect it.

This change adds the header-only boost dependency to emper.
https://mesonbuild.com/Dependencies.html#boost
The header-only dependency is enough to build emper default configuration.

When linking against boost is required we use the 'modules' karg.

[Dispatcher] replace deprecated pthread_yield with sched_yield

See merge request !302

Compilation with gcc on ubuntu 21.10 fails because pthread_yield is
apparently deprecated and should be replaced with sched_yield.

gcc --version
gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0

properly cancel future callbacks

See merge request !297

* Document data races of a future's state.
* Get and set a Future's state only through methods. This helps to
  add possibly needed atomic operations.
* Use atomics to get/set cancel and prepare state in IO_SINGLE_URING vaiant
* Add more IO debug messages
* Use the BPS of Futures with callbacks similar to those of forgotten
  ones to signal their preparation. The preparation mark the
  last moment where the Future is used in EMPER and after that the memory
  can be dropped.
  ATTENTION: This means not that the used resources of the IO request
  can be dropped. The kernel may still use a supplied buffer for example.
* Fix Future chain cancellation in SubmitActor

Currently canceling Futures would never happen because we
issued the cancel request only with the pointer of the future.
This works more by coincidence than by design because
the PointerTags::Future tagged onto the submitted future pointer is 0.

This does not work for callbacks because they are tagged with a
PointerTags != 0 and they don't use their callback pointer rather
than the future pointer.

Fix this by exporting the tagging from IoContext::prepareFutureChain
into IoContext::createFutureTag and use this when submitting a cancel
sqe.

Warn the user that they have to manually take care of the memory safety
of the callback because we can not await the callback in Future::cancel.

Add a test case to CancelFutureTest.

[Common] introduce a CACHE_LINE_SIZE define

See merge request !299

[SpuriousFutexSemaphore] futex are 32 bits on all platforms

See merge request !300

This define will be used in future patches.

Make Scheduler within Runtime public API

See merge request !298

The Runtime class was never a good place for inRuntime(): due its
central role in EMPER's architecture, it causes easily include
cycles. Furthermore, the API was not ideal, once we would move Runtime
into emper::, it would become emper::Runtime::inRuntime().

We declare emper::Emper::inRuntime and emper::Emper::assertInRuntime()
as static struct functions to avoid multiple definitions, and then use
a constexpr function "alias" to have those functions available in the
emper:: namespace.

[IO] overhaul SQPOLL support

See merge request !210

[CI] print the number of available CPUs

See merge request !290

[qsort] fix implicit widening clang-tidy error

See merge request !292

[ConcurrentNetworkEchoTest] add optional computation per echo

See merge request !293