Modernize code

Document the precise behavior of VoxelRayTrace::betweenPoints (#74)

Facing: improved error message for rotate()

phpunit-shim is unmaintained since March

Vector3: added zero() static method

Drop everything below PHP 7.4

Constrain PHP to ^7.2 || ^8.0

Update phpstan/phpstan requirement from 0.12.39 to 0.12.40 (#17)

phpstan: go with level 8 (no changes needed)

Vector3: fix parameter types for setComponents()