[1.x] Rework pulse:check command

[timacdonald]

The current implementation of the pulse:check command is based on our earlier version of Pulse. Due to this, there is a lot of things that feel clunky and don't work as reliably as they could.

This PR rethinks the command and also how recorders that interact with the shared beats can work.

It also allows the command to run a single time when run within a Laravel Vapor's scheduler.

Improvements

Recorders previously had to do some modulus math if they only wanted to record every now an then. The timeframes were limited to 5 second increments. For example, if we wanted our recorder to take a snapshot every 15 seconds we would do the following...

public function record(SharedBeat $event)
{
    if ($event->time->second % 15 !== 0) {
        return;
    }

    // Record...
}

You now may use the much more reliable Throttling concern, that ships with Pulse, to throttle recording to a max of every 15 seconds. The throttled duration can now be any arbitrary interval, although the beat will only be triggered roughly once per second.

This makes recording on any given interval much more reliable than it was previously, which could miss intervals if listeners took too long.

use Concerns\Throttling;

public function record(SharedBeat $event)
{
    $this->throttle(15, $event, function () {
        // Record...
    });
}

For shared beats this will throttle to the current server. For isolated beats this will throttle across servers.

Implementation notes

• The lastSnapshotAt has been removed. This was not always accurate, and sometimes it was simply a lie. For example, the first time you run the command it will tell you it was run 5 seconds ago, which it was not.
• The 5 second interval is now arbitrary. It was important in our early days, but no longer makes sense.
• The time rounding was important in previous iterations of Pulse, but is no longer relevant.
• The "now" value is captured before we dispatch events, rather than before we potentially sleep. This was just bad regardless.
• Beats are now triggered roughly once a second.