Tags

- added support for PHP 8.x, bumped minimal version to 7.4
- added support for Guzzle 7.x
- updated missing typings
- usage of Composer 2.x for development purposes
- updated development tools: `phpunit` and `dealerdirect/phpcodesniffer-composer-installer`

Additionally CI/CD process has been extended with `phpstan` and `phpcs` tools.