It’s easy to appreciate the investment of time and effort that go into constructing any period piece, a balancing act between capturing the atmosphere of a bygone age and finding a middle ground equally satisfying to both the casual viewer and the history buff. And so, brimming with more than a handful of nods to spiritual siblings “The Tudors” and “The Favourite” both in tone and ambiance, the new STARZ limited series “Mary & George” finds the right mix and a seat at the table with relative ease.