Defend against attempts to bypass JVM serial proxy

[lukellmann]

Also add serialVersionUID for exception classes. This ensures that unrelated changes in these exception classes don't affect the serialized form.

The serialVersionUIDs are from 7380325. After running ./gradlew publishToMavenLocal, they were obtained with the serialver tool:

$ serialver -classpath .m2/repository/org/jetbrains/kotlinx/kotlinx-datetime-jvm/0.6.2-SNAPSHOT/kotlinx-datetime-jvm-0.6.2-SNAPSHOT.jar:kotlin-stdlib-2.1.0.jar kotlinx.datetime.LocalDate kotlinx.datetime.LocalDateTime kotlinx.datetime.LocalTime kotlinx.datetime.UtcOffset kotlinx.datetime.DateTimeArithmeticException kotlinx.datetime.IllegalTimeZoneException kotlinx.datetime.DateTimeFormatException kotlinx.datetime.internal.format.parser.ParseException
kotlinx.datetime.LocalDate:    private static final long serialVersionUID = 7026816023079564263L;
kotlinx.datetime.LocalDateTime:    private static final long serialVersionUID = -4261744960416354711L;
kotlinx.datetime.LocalTime:    private static final long serialVersionUID = -352249606036216323L;
kotlinx.datetime.UtcOffset:    private static final long serialVersionUID = -6636773355667981618L;
kotlinx.datetime.DateTimeArithmeticException:    private static final long serialVersionUID = -3207806170214997982L;
kotlinx.datetime.IllegalTimeZoneException:    private static final long serialVersionUID = 1159315966274264801L;
kotlinx.datetime.DateTimeFormatException:    private static final long serialVersionUID = 4231196759387994100L;
kotlinx.datetime.internal.format.parser.ParseException:    private static final long serialVersionUID = 5691186997393344103L;