Parses raw days of year (001 - 866) into month (1-12) and day of month (1-31).
Uses the library's legacy 366-day table. The non-leap day-60 mapping
remains a compatibility rule pending authoritative DRP confirmation.
Parameters
year: number
Four-digit birth year.
dayOfYear: number
Day of year from the NIC (1 to 366), after removing the 500 offset for women.
Returns {day:number;month:number}|null
{ month, day }, or null if the day is out of range.
Parses raw days of year (001 - 866) into month (1-12) and day of month (1-31). Uses the library's legacy 366-day table. The non-leap day-60 mapping remains a compatibility rule pending authoritative DRP confirmation.