feat(php-tools): add phpstan and phpunit

[jokesterfr]

Questions	Answers
Description?	Would be very useful to rely on flashlight to perform module testing. It is often complexe to get tools up to date AND compatible with a target PHP version, and this would be brung to PrestaShop Flashlight as a new feature.
Type?	new feature
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes #{issue URL here}, Fixes #{another issue URL here}
Sponsor company	PrestaShop
How to test?	check either of these commands: composer, phpunit, phpstan from the command line