Improve input validation for compound ABI types

The ABI router does not currently provide input validation for compound types. This issue is to improve the situation with the following additions:

* For static compound types, verifying the length of input values would be a low-cost but welcome validation step. (For static compound types of dynamic values, we could only verify that the minimum length if met.)

* For all compound types, provide a `verify()` method which will verify the validity of the value at runtime, or panic if the value is invalid. Depending on the depth and dynamic-ness of a type, this may be an expensive operation, which is why it's better for users to explicitly call it if they need it, as supposed to always including this code.