Outside of Mystic Theurge, I am unaware of anything that would provide simultaneous arcane and divine spell casting. Which is probably a good thing. The designing of such a class sounds like a nightmare to me. Not to mention, a spell cast by an arcane or divine caster (such as Detect Magic) has no difference beside the power source. With the exception of (mostly) exclusive spells for their respective lists, it's really the special class features that differentiate between the casting types. If such a class does exist, you're most likely going to find its home-brewed.