Parameter type checking should allow `int`s where a `float` is required

With JSON, it's really easy to end up with an `int` rather than a whole number `float` -- the difference is just in the period, and e.g., `"{:.0f}".format(3.0)` will produce a "3". A number of scripts also exist that were written before the type-checking got stricter and casually send whole numbers, especially "0", in a way that JSON parses as ints, causing Coco to reject them as malformed requests.

Instead, we should have special handling for this case and just convert an int to float silently.