security: write more fuzzers and perform continuous fuzzing

[odeke-em]

Implementation ideas

For general security and ensure that we build stronger trust, let's write a bunch of fuzzers for as many critical methods. Just from my random auditing and weekend play-time I wrote some fuzzers and found like 5 issues: #3727, #3728, #3729, #3730, #3731 from less than 3 hours of poking around; so much more lurks and for a billion dollar ecosystem it is rightful that we have continuous fuzzing with oss-fuzz.com: I shall handle getting Celestia petitioned to be accepted and have continuous fuzzing 24/7 at no cost.

/cc @Wondertan @liamsi @musalbas @cristaloleg