******TARDIS-SIZED SPOILERS!****** Last we saw the new Doctor (Ncuti Gatwa), he’d just ‘bi-generated’ from the 14th Doctor (David Tennant) atop UNIT Headquarters as they battled the Toymaker (Neil Patrick Harris) together in Special #3: “The Giggle.”  With Doctor 14 surviving the split and living in a state of semi-retirement with the Noble family, this 15th Doctor…