Python: fix ValueError: day of month directive '%d' may not be used without a year directive

Python 3.15 raises a ValueError whenever strptime() uses the %d (day of month) directive without a year directive, breaking code that previously parsed month-day strings without a year. This behavior was deprecated in Python 3.13 with a DeprecationWarning, and the root cause is that strptime() defaulted to 1900 (a non-leap year), making February 29th unparseable. The fix is to append a leap year (e.g., 2000) to both the input string and the format string, ensuring all dates including Feb 29 parse correctly across all Python versions.