As a contrast to some of our scattered-theme game roundups of the last several weeks, the latest iPhone Gems looks at titles from two different genres: action puzzle games, and shooters. More importantly, there are actually a couple of diamonds in this week’s collection: Wooden Labyrinth 3D is our top pick of the week in the puzzle genre, with Heavy Mach an impressive selection for fans of shooters. Both do an unusually good job of showing off…