improve the fuzzer

[redianthus]

Ideas:

• [ ] ESFuzzer: An Efficient Way to Fuzz WebAssembly Interpreter;
• [ ] Random Testing of the WebAssembly System Interface;
• [ ] WasmCFuzz: Structure-aware Fuzzing for Wasm Compilers.

Easy things to start with:

• [x] https://github.com/OCamlPro/owi/issues/179