Migrate Gradle buildscripts to Kotlin script

[EnnuiL]

Crooked Crooks and Pause Music on Pause have proven to be successful adaptations of Up's Ok Zoomer multiloader buildscript so far, therefore Ok Zoomer should ditch Groovy and go full .kts

(PS: this is purely technical stuff that will not affect the mod at all, Ok Zoomer will never migrate its codebase to Kotlin unless a miracle happens and both loaders begin bundling the super-heavy standard libraries (that and proper Minecraft bindings are created that aren't maintained by a racist))