Limiting the size of ingress queues

The Diffusion Layer currently defines limits on buffers used for pipelining as a combination of the max size of the buffer and the max size of each entry within the buffer. The current definitions are hard-coded, but they have been manually derived from the current parameters of the `Cardano` `mainnet`.

This task is to work out where the information should come from, how much of it should be dynamic (it's all static at the moment), and where each of these definitions should belong in the package/module hierarchy.