Investigate alternative fuzzing engines

[brson]

What problem does your feature solve?

The Soroban fuzzing experience could be better, but probably can't be improved much without switching to a different fuzzing engine.

Soroban has support for fuzzing via cargo-fuzz. This support depends on libfuzzer, an LLVM project which is in maintenance mode and sees no improvements. The cargo-fuzz/libfuzzer user experience is primitive.

It also currently requires a workaround on macos.

What would you like to see?

Investigate alternative fuzzing engines:

• https://github.com/loiclec/fuzzcheck-rs
• https://github.com/AFLplusplus/LibAFL

It's unclear how mature these are and whether they are viable for Soroban. We just need to take the first step and give them a try.