Decrease CPU usage of datetime by events

[Bartosz Kosiorek]

Currently in ./src/wakeup-timer-mainloop.cpp
the g_timeout_add_full function is used to call intervals:

        const auto now = m_clock->localtime();
        const auto difference_usec = g_date_time_difference(m_wakeup_time.get(), now.get());
        const guint interval_msec = std::abs(difference_usec) / 1000u;
        g_debug("%s setting wakeup timer to kick at %s, which is in %zu seconds",
                G_STRFUNC,
                m_wakeup_time.format("%F %T").c_str(),
                size_t{interval_msec/1000});

        m_timeout_tag = g_timeout_add_full(G_PRIORITY_HIGH,
                                           interval_msec,
                                           on_timeout,
                                           this,
                                           nullptr);
More information:
 https://developer.gnome.org/glib/stable/glib-The-Main-Event-Loop.html#g-timeout-add-full

The grouping of timers to fire at the same time results in a more power and CPU efficient behavior
That's why I would recommend to use:
   g_timeout_add_seconds_full ()
instead

[Charles Kerr (charlesk)]

Good suggestion! Thanks Bartosz.