Conditionally ignore tests and better stack traces for fixtures

### Suite - Exceptions in fixtures are wrapped by an `AssertionError` to facilitate understanding the failure path (!205) - Added `Ignored.If` and `OnlyIf` to conditionally ignore tests (!206) ### Gradle compatibility - Fixed a bug in `gradle.properties()` (!209) ### KotlinX.Datetime compatibility The `:compat-kotlinx-datetime` module has been deleted. All its functionality has already been moved to `:suite` using the `kotlin.time` package multiple releases ago. The module is still available on MavenCentral but will not be updated in the future.