Track coverage of fuzz targets

[Crypt-iQ]

• We should get a visual output of the fuzz coverage for each target individually and combined. This can let us know if certain branches aren't taken.
• This could be done via go coverage files.
• Once we are fuzzing continuously, we can then take the coverage files and update a website daily with updated fuzzing coverage. In my mind, it would sort of look like this bitcoind fuzzing coverage webpage I made: https://crypt-iq.github.io/19379_fuzz_cov/

[Crypt-iQ]

We should be automatically tracking changes to coverage in CI