Function looks_like_drg 

pub fn looks_like_drg(text: &str) -> bool

Cheap sniff: does text look like .drg (or headerless two-column CSV of the same shape)? Finds the first two data rows and checks that one of the two columns is ascending between them — a bounded scan that does not allocate the full points vector (unlike calling parse_drg and checking is_ok()), so it’s cheap to use as a pre-check before committing to a full parse.