Switch to PHP 8.0 syntax via Rector

[morozov]

Q	A
Type	improvement

The following configuration was used to make the changes:

<?php

declare(strict_types=1);

use Rector\Config\RectorConfig;
use Rector\Core\ValueObject\PhpVersion;
use Rector\Set\ValueObject\SetList;

return static function (RectorConfig $rectorConfig): void {
    $rectorConfig->paths([__DIR__ . '/src', __DIR__ . '/tests']);
    $rectorConfig->sets([SetList::PHP_80]);
    $rectorConfig->phpVersion(PhpVersion::PHP_80);
    $rectorConfig->phpstanConfig(__DIR__ . '/phpstan.neon.dist');
};

I reverted the addition of implements Stringable as I believe that relying on __toString() in the cases except for logging is an anti-pattern. I'd rather get rid of these methods in the codebase.

We can enforce the above rules on CI as the next step once they are supported by the coding standard.

[derrabus]

I love how the code looks after this PR. 🥳