Fix: Fix dangling timer when lazy connection closes with pending commands.
(#105 by @clue)
Improve test suite and add .gitattributes to exclude dev files from exports.
Prepare PHP 8 support, update to PHPUnit 9 and simplify test matrix.
(#96 and #97 by @clue and #99, #101 and #104 by @SimonFrings)
