Rename the macro used to build up the debug message, to better reflect
its generality.
It can be used anywhere to build a string with C++ stream formatting.
std::string s = EMPER_BUILD_STR("foo = " << 1 " , bar = " << bar(42));

Since WDBG was the only log macro without a terminating newline, which
was in fact broken according to flow, we can remove it and the new line
handling code in the LOG macro.

Using an AlarmFuture blocks the Fiber executing Actor::waitUntilIdle,
freeing its current worker and thus preventing life-locks.
Where all workers are sleeping except one.
Which executes the Actor::waitUntilIdle Fiber causing a starvation of
the actual Actor.

We are unable to switch to C++20 until
https://github.com/mesonbuild/meson/issues/8084 is fixed.

In debug builds, the schedule() method is now guarded by an assert(),
as due to this change, the schedule() method will no longer work from
everywhere.

This also improves the worker sleep method.

And fix the #include issues reported by the newer IWYU version.

This should not change much, but ensure that this method is also
invoked in the test (even though it is not explicitly tested).

The CPS already gets incremented by the
SynchronizedFiber. Initializing the CPS with FIBER_COUNT means that
the CPS will never become ready.