Implement use_type: "tuple" #24

Currently tuples are only used when all source arrays have the same length and combining the shapes of the array would lose type information. E.g. you can end up with [["a", 1], ["b", 2]] is inferred to Array<[string, number]>, but [[1, 2], [3, 4]] is inferred as number[][].

We already have the hint use_type: "map". We should similarly have use_type: "tuple" and with that make it possible to end up with types like [string, string] and [number, number, number?].