Test framework for "chunked" designs

A lot designs fundamentally work on datastructures that are slowly fed into the circuit. For example, a circuit on matrices might receive and send matrices row-by-row. It would be nice if we could define a model that works on the whole structure, while "cutters" and "mergers" would produce the inputs for a circuit based on the whole structure, and vice versa. All while neatly fitting into a test framework.

The issue names no files, tests, or entry points to start from. First map the existing test framework and protocol abstractions, then determine how a whole-structure model, cutters, and mergers should fit together; done would mean the chunked design is supported by the test framework.

Written by the indexing model from the issue text.