Use `azjezz/psl` instead of `beberlei/assert`

[mariosimao]

You might want to use azjezz/psl for improved type inference, in future: I've used beberlei/assert and webmozart/assert extensively over the years, but @azjezz's work is just so much better, long-term

Originally posted in #6 (comment)

[azjezz]

for reference, you can look at Roave/BackwardCompatibilityCheck#306 and laminas/automatic-releases#138