Make legacy XmlConvert date parsing formats explicit

Replace resolved XmlConvert.ToDateTime(string) with the exact historical 24-format array overload. Preserve input evaluation, parsing rules and failure handling without selecting a serialization mode. The explicit format array allocates per call; review hot paths before choosing this opt-in compatibility port. Leave other overloads/types, custom/dynamic conversions, named arguments, method groups, lambda/query bodies, generic declarations and snapshots unchanged. Outside version composites.