Coterra Energy is kicking the tires on what would be one of the biggest U.S. shale mergers in years, holding talks about a possible combination with Devon Energy, according to people familiar with the matter. Nothing is signed, nothing is guaranteed, but the market liked the idea enough to send shares of Coterra Energy sharply higher on the day. The deal would be a classic all-stock shale mashup: two midsize operators with large footprints in the Permian Basin trying to bulk up as oil prices sit stubbornly around $60 a barrel. Coterra carries a…