Fix for kotest 0.5.0+, upgrade gradle, kotlin

[dhoepelman]

Due to removing the variance from Invalid (it now extends ValidationResult<Nothing>) in kotest 0.5.0 this library has been broken with newer konform versions.

Interestingly enough it crashes the kotlin compiler itself, so will see if I can scrounge up the error and report it to Jetbrains.

This PR fixes that and upgrades konform to the latest 0.6.2.
This also allows me to start using kotest in the project itself.

@sksamuel I'm the new maintainer of konform. Might be interested in performing some maintenance work on this if I get around to it. Mind giving me write access to the repo so I can open PRs directly against it instead of against a fork?

Things I see:

• Upgrade to Kotlin 2
• Adding all kotlin native targets, konform added all multiplatform targets
• Add/improve matchers
• Upgrade gradle (might leave this to kotest maintainer(s) as this is a kotest project so it matches that setup)

[dhoepelman]

Had to also upgrade kotlin and gradle to get the build to work.

[sksamuel]

I've given you write access @dhoepelman

[dhoepelman]

@sksamuel thanks for access and merging!