chore: some improvements around array typehints

[keradus]

as we see, we shall not blindly apply, but rule is great to find the cases and pre-fill the fix.

unfortunately, PHPStan is not able to detect violations. (so we cannot apply the rule, run Stan, and assume all good if there was no error)

[coveralls]

coverage: 94.753%. remained the same
when pulling 5d93602 on keradus:array2list
into d15cfea on PHP-CS-Fixer:master.

[julienfalque]

unfortunately, PHPStan is not able to detect violations. (so we cannot apply the rule, run Stan, and assume all good if there was no error)

I think PHPStan checks list constraints when enabling bleeding edge, which is our case.