Fix for DateTimeException: Invalid date 'FEBRUARY 31'

[Sheryv]

This PR fixes 2 issues in calev-core:

1. Prevents throwing DateTimeException: Invalid date 'FEBRUARY 31' :

   The following example

       val expression = CalEvent(AllWeekdays, date(All, 2.c, All), time(0 #/ 6, 0.c, 0.c))
   
       val next = expression
         .nextElapse(OffsetDateTime.parse("2024-01-31T18:00+01:00").toZonedDateTime)
         .get
   
       assertEquals(next, ZonedDateTime.parse("2024-02-01T00:00+01:00"))

   in the current library version, will throw

   java.time.DateTimeException: Invalid date 'FEBRUARY 31'
   
       at java.base/java.time.LocalDate.create(LocalDate.java:459)
       at java.base/java.time.LocalDate.of(LocalDate.java:275)
       at com.github.eikek.calev.internal.DefaultTrigger$Date.toLocalDate(DefaultTrigger.scala:96)
       at com.github.eikek.calev.internal.DefaultTrigger$Calc.maxValue(DefaultTrigger.scala:197)
       at com.github.eikek.calev.internal.DefaultTrigger$Calc.atStartBelow(DefaultTrigger.scala:221)
       at com.github.eikek.calev.internal.DefaultTrigger$Calc.atStartBelowCurrent(DefaultTrigger.scala:227)
       at com.github.eikek.calev.internal.DefaultTrigger$.run(DefaultTrigger.scala:83)
       at com.github.eikek.calev.internal.DefaultTrigger$.go$1(DefaultTrigger.scala:40)
       at com.github.eikek.calev.internal.DefaultTrigger$.next(DefaultTrigger.scala:51)
       at com.github.eikek.calev.CalEvent.nextElapse(CalEvent.scala:44)
       at com.github.eikek.calev.CalEventTest.$anonfun$new$45(CalEventTest.scala:103)
       at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
   

   Adding range check for the day field fixes that particular problem

2. Prevents application freeze when negative count is passed to Trigger.nextRepeat() by adding validation

[eikek]

Thank you very much!