so-5.5.0: Timer thread factories

Since v.5.5.0 the Timer Thread Template library is used for timers implementation. The timertt provides several timer mechanisms and user can choose which one will be used with SObjectizer Environment.

There are several factory function for timer mechanism creation: so_5::timer_wheel_factory, so_5::timer_list_factory and so_5::timer_heap_factory. Any of them can be used in tuning SObjectizer Environment parameters. For example:

so_5::launch(
    []( so_5::rt::environment_t & env )
    {
        // Some initialization stuff...
    },
    // SObjectizer Environment parameters tuning.
    []( so_5::rt::environment_params_t & params )
    {
        // Use timer_wheel mechanism with wheel size 10000
        // and timer step size of 5ms.
        params.timer_thread(
            so_5::timer_wheel_factory( 10000, 
                std::chrono::milliseconds(5) ) );
        ...
    } );

By default the timer_heap mechanism is used. But if your application uses a lot of timers (millions or tens of millions or even more) then timer_wheel must be considered as more appropriate for big amount of timers.