Function is_date_time_pattern 

pub fn is_date_time_pattern(pattern: &str) -> bool

Check whether a number-format pattern is suitable for use as a date/time pattern.

This is a minimal token scanner (not a full nfp parser). It rejects patterns that contain numeric-only tokens such as 0, #, ?, %, the text placeholder @, scientific notation (E+0, E-0) or fractions (?/?). Quoted literals, escaped characters, bracketed expressions (colors, locales, elapsed time) and common date/time separators are allowed. An empty pattern is allowed.