Feature: Add new delay() function to delay program execution.
(#72 by @clue)

echo'a'; Loop::addTimer(1.0, function (){echo'b'}); React\Async\delay(3.0); echo'c'; // prints "a" at t=0.0s// prints "b" at t=1.0s// prints "c" at t=3.0s

Update test suite, run tests on PHP 8.2 and report failed assertions.
(#59 and #75 by @WyriHaximus and #68 by @clue)