Const checks or tests to ensure messages fit in buffers

[andrewdavidmackenzie]

In porky in particular (as buffers are statically allocated and of fixed size), implement some checks to ensure that buffers are big enough to take the serialization of the messages that pass.

Probably need to generate a lot of variants of each message type, serialize them in tests and check versus some constant - that is used in the code for the size of static buffers.