Add support for diffing two fuzz-introspector runs

[DavidKorczynski]

The goal of fuzz introspector is by and large to make it easier to improve a fuzzing set up for a given software package. At the moment fuzz introspector only focuses on a single analysis, whereas, in order to determine if an improvement was successful one has to compare two fuzz introspector runs. As such, we should have some features that make it possible to compare fuzz introspector analyses and specifically make it easy to highlight improvements/regressions.

[DavidKorczynski]

The plan for doing this is exporting lots of the data generated by fuzz introspector into a json format (https://github.com/ossf/fuzz-introspector/blob/main/src/fuzz_introspector/json_report.py) and then build a diffing tool based on that.

[DavidKorczynski]

A thought in this context is that it would be good to start making the code more object oriented and in particular some form of broader "Fuzz Introspector Report" class, which will make certain things such as serializing data and comparing data more intuitive from a code-level perspective. I don't think this should hold up making some initial progress in this context, but, medium term we should aim for something more object oriented.