Fix PSL 2 support

[veewee]

Bug Report

Q	A
BC Break	no
Version

See new PRs:
#33, #34, #35

• Failing unit tests - assertions not working properly
• Autoload build failure due to usage of old function
• PSL psalm plugin not being registered

Currently PSL 2 is not supported by the codebase.
PSL 1 is not compatible with PSL 2.
Since PSL2 is only supporting PHP >=8.1 and we still support PHP 8.0 - it currently makes no sense to upgrade.
Once PHP 8.2 lands or PHP 8.0 support ends in this package, we can upgrade the internal API to use PSL 2.

In the meantime, PSL1 is still compatible with both PHP 8.1 and 8.0