Usage of Java's `LocalTime` instead of Kotlinx's

[Jolanrensen]

Convert toLocalTime uses Java's LocalTime instead of Kotlinx's. We should use kotlinx.datetime.LocalTime instead of java.time.LocalTime if we ever want to go multiplatform and just for general consistency.

parse uses even more java.time versions: LocalDate, LocalDateTime, LocalTime, as well as java.time.format.DateTimeFormatter, but I'm not sure if that can be replaced.