[apps] Use sync.h instead of atomic.h in the verbose module.

[maxsharabayko]

The atomic.h header of the SRT project can include sync.h header in the following case:

#if defined(ATOMIC_USE_SRT_SYNC_MUTEX) && (ATOMIC_USE_SRT_SYNC_MUTEX == 1)
   #include "sync.h"
#endif

It leads to the compilation error because sync.h includes atomic.h and later atomic_clock.h:

[ 60%] Building CXX object /apps/socketoptions.cpp.o
In file included from /srtcore/sync.h:1069,
                 from /srt/srtcore/atomic.h:104,
                 from /srt/apps/verbose.hpp:15,
                 from /srt/apps/socketoptions.cpp:12:
/srt/srtcore/atomic_clock.h:25:5: error: 'atomic' does not name a type; did you mean 'atoi'?
     atomic<int64_t> dur;
     ^~~~~~
     atoi
/srt/srtcore/atomic_clock.h: In constructor 'srt::sync::AtomicDuration<Clock>::AtomicDuration()':
/srt/srtcore/atomic_clock.h:30:37: error: class 'srt::sync::AtomicDuration<Clock>' does not have any field named 'dur'
     AtomicDuration() ATR_NOEXCEPT : dur(0) {}
                                     ^~~
/submodule/srt/srtcore/atomic_clock.h: In member function 'srt::sync::AtomicDuration<Clock>::duration_type srt::sync::AtomicDuration<Clock>::load()':
/srt/srtcore/atomic_clock.h:34:23: error: 'dur' was not declared in this scope
         int64_t val = dur.load();
                       ^~~
/srt/srtcore/atomic_clock.h:34:23: note: suggested alternative: 'dup'
         int64_t val = dur.load();
                       ^~~
                       dup

The verbose module uses srt::sync::atomic<bool> lockline, so makes sense to include sync.h straight away.

Affected SRT versions: 1.5.4 RC.0, RC.1 (after PR #3004).

[maxsharabayko]

Now when including verbose.hpp from a different app (e.g. xtransmit) the ENABLE_STDCXX_SYNC has to be properly defined in xtransmit as well 😞
Well, most of the time this should not be a problem.

[maxsharabayko]

What about just using <atomic>? 🤔
There are common things referring to atomic, which can't use just any atomic. There are some things referring to formatting and locking for printing, especially in verbose, and conflicts may arise based on that.