The Mets offensive stats read like a hitting coach’s worst nightmare: fewest runs scored in the majors, as well as the lowest on-base percentage, slugging percentage and OPS, entering play Tuesday. After being swept in a doubleheader by the Rockies on Sunday, when the Mets scored one run, Carlos Mendoza said, “I don’t think I’ve ever seen anything like this.” Hitting coach Troy Snitker wouldn’t go that far when asked about the offense, but the former Astros hitting coach acknowledged he couldn’t recall an extended period of poor performance like the one the Mets have gone through in the first month of the season. “As a hitting coach, and with hitting in general, you go through these unfortunate stretches during a season,’’ Snitker said before the series opener against the Nationals at Citi Field.…