Update Kotlin version

[mipastgt]

Would you mind updating Kotlin to its latest version? Just changing 2.1.20 to 2.2.21 in the files

1. config.toml.template
2. library/build.gradle.kts
3. Tester.px

should be enough, if I haven't missed anything. With these changes everything still compiles and runs.

[IntegralPilot]

Thanks for picking this up, I didn't realise a new version had been realised! Done in 9dddf17 :)

[mipastgt]

Your update is wrong. It must be 2.2.21 and not 2.1.21.
https://github.com/JetBrains/kotlin/releases/tag/v2.2.21