Humane started shipping its Ai Pin in April.NurPhotoThe latest attempt to dethrone the smartphone arrived this week.Humane, a startup founded in 2018, released an AI pin that aims to offer an alternative.Reviews suggest it's far from a smartphone-killer, however.Silicon Valley is having a hard time figuring out what a post-smartphone future might look like.Ever since Steve Jobs introduced the world to the iPhone almost two decades ago, back in 2…