Add a testutil function that will fuzz random valid and invalid blocks

[evan-forbes]

It would be useful for us and for node to have a function that can generate both random valid and invalid blocks.

[Ray-Escobar]

hi, i want to help with this. I assume the type to fuzz is tendermint/types Block ?

[evan-forbes]

closing in favor of #1535

@Ray-Escobar this is a rather beefy issue that we are currently already working on to essentially test every possible corrent thing in celestia-app, so I'm this has turned into an issue that is no longer a good first issue. Thanks for your interest though! We have other good first issues that we would also appreciated 🙂

[Ray-Escobar]

thanks @evan-forbes will be scoping around, so you will see my name pop-up somewhere else.