[10.x] Adds Countable to the InvokedProcessPool class.

[xiCO2k]

This PR adds a capability to retrieve the total of invokable processes on a pool.

Usage

$pool = Process::pool(function (Pool $pool) {
    $pool->command('sleep 2; echo 1');
    $pool->command('sleep 3; echo 2');
    $pool->command('sleep 1; echo 3');
})->start();

while ($pool->running()->isNotEmpty()) {
    $completed = count($pool) - count($pool->running());
    $this->components->info(sprintf('%d of %d processes completed!', 
        $completed, 
        count($pool)
    ));
}

Cheers.

[taylorotwell]

How about just implementing Countable on the InvokableProcessPool so we can do count($pool)?

[xiCO2k]

Even better, will make the change.

[xiCO2k]

Done ✅

[taylorotwell]

Thanks