Fuzz targets

[darosior]

We agreed upon having:

• A fuzz target for FromScript(). That's fuzz: add a fuzz target for Miniscript decoding #78. That's Add script/string roundtrip fuzz tests #106.
• A fuzz target for random node generation that's "dumb" (does not help the fuzzer to generate valid nodes). That's Pseudo-random node generation from fuzzer's input using a strict binary encoding #100.
• A fuzz target for random node generation that's "smart" (does help the fuzzer to generate valid nodes). That's Add type-driven fuzzer #105
• A fuzz target for FromString(). That's Add script/string roundtrip fuzz tests #106

[darosior]

Now, the work on the random fuzz targets was done on different forks of this Bitcoin Core branch bitcoin/bitcoin#24149, which is itself not up to date due to verbose renames and refactoring during the review of bitcoin/bitcoin#24147.

I think we should update this repo with the various refactorings from the Bitcoin Core PRs, and open PRs for each fuzz target here to centralize discussions.

[darosior]

It's now complete! 🎉