I've implemented about 13 different fuzzers that each fuzz different parts of the Bitcoin core source code. Collectively these result in much more code coverage than src/test/test_bitcoin_fuzzy.cpp but are not exhaustive (yet).

I could not find any issues despite running the fuzzers for a long time.

If you want it, I'll make a pull request. I'm also willing to work together with someone who has more intimate knowledge of the Bitcoin core source code to complement the current set of fuzzers.