Written by DCist contributor Meghan Welsh Though professional dancers train for years to achieve perfect technique, there is one rule that trumps everything else when it comes to performing: make it look effortless. CityDance Ensemble’s performance of “Eclipse” on Sunday evening at the Music Center at Strathmore more than accomplished this feat. The concert was part of the D.C.-based contemporary repertory dance company’s “In the Studio” concert series, which transforms a dance studio into a…