Add typing

[kalombos]

Нужно добавить типизацию, также добавить линтер на проверку типизации в ci Удобно делать типизацию итерационно, по файлам, после #223

It needs to add typing, also add a linter to check typing in ci. It is convenient to do typing iteratively, by files, after #223

[rudyryk]

This would be great! And as typing is not forced we are not forced to make linter 100% happy from the start, so it can perfectly work with a single file and incomlete annotations as well. We'll just gradually work on linter complaints.