A bunch of maintenance to bring this up to date

Replaced Kobalt with Gradle
Updated dependencies and fixed code that broke with the updates
Replaced test data set with the latest zip from https://github.com/PokeAPI/api-data
- also unpacked the zip so we're not committing a binary file to git
Fixed any broken tests on the latest data
- this was mostly test fixes, except making ItemSprites.default nullable
Attempt to set up publishing to Github Packages (untested)

PokeAPI / pokekotlin