Date Format Token Validation

What: Implemented validation for deprecated uppercase date format tokens

Details:

• Function vB9() at line 458852 now validates year tokens (Y, YY, YYYY)
• Warns users when using deprecated uppercase tokens that should be lowercase
• Prevents confusion between ISO week-numbering years (Y) and calendar years (y)
• Previously stubbed in v2.0.45 (vB9 = () => {} at line 458887), now fully implemented
• Part of date-fns Unicode token validation system
• Evidence: Implementation added at vB9() at line 458852, used in format validation at line 458914