WW3_PRNC does not handle 360 day calendars

[ukmo-ccbunney]

Describe the bug
WW3 can be run using a 360 day (climate) calendar where each month has an equal number of days (30).
However, the WW3_PRNC program does not have this functionaliry meaning it is not possible to pre-process input files from netCDF files, even if calendar type is set to 360day in the mod_def file.

To Reproduce
Generate mod_def with 360day calendar. Try running ww3_prnc on a input file with 30 day months for February.
The last day that will be processed for February is the 28th (or 29th on a leap year).

Expected behavior
Missing forcing data.

Additional context
We need to handle other calendar types when decoding dates in ww3_prnc, here:

WW3/model/src/ww3_prnc.F90

Lines 798 to 808 in 3952826

	IRET=NF90_GET_ATT(NCID,VARIDTMP,"calendar",CALENDAR)
	IF ( IRET/=NF90_NOERR ) THEN
	WRITE(NDSE,1028)
	ELSE IF ((INDEX(CALENDAR, "standard").EQ.0) .AND. &
	(INDEX(CALENDAR, "gregorian").EQ.0)) THEN
	WRITE(NDSE,1029)
	END IF
	IRET=NF90_GET_ATT(NCID,VARIDTMP,"units",TIMEUNITS)
	CALL CHECK_ERR(IRET)
	CALL U2D(TIMEUNITS,REFDATE,IERR)
	CALL D2J(REFDATE,REFJULDAY,IERR)