feat: add `memoize.lua`.

[UserIsntAvailable]

Credits goes to: https://github.com/kikito/memoize.lua

This add a memoize function that lets users cache return values from a function passed as an argument.

It is pretty much a copy paste of the that kikito already wrote, with some changes to follow the stylua formatting.

This technically could go to functional.lua, but it would be probably better to have it in its own file.