Draft: Add simple footprint testing utility

This is a very early draft of some thin framework for executing footprint generators as part of the test suite and get CI executing the generators and checking a subset of the output. It includes a naive equality test for the FP data (by comparing the S-Exp data directly)

The actual equality test isn't really the focus here as it should be made a lot more robust (e.g. most element ordering does not matter). It might also become image-diff-based if the performance implications aren't too dire.

This is mostly to get some early comments on the general approach of putting the test fixtures near each generator and parameterising somehow with the various inputs.

For now, this only tests a single generator as an example (Converter_ACDC_DCDC)