Add LibAFL-Targets Crate as a Dependency

The libafl_targets crate provides target-specific functionality and runtimes for various instrumentation mechanisms designed to be used with libafl. In our case, it provides an easy way to interact with SanitizerCoverage. We'll go in depth on our instrumentation later, for now we'll just add the crate to our Cargo.toml:

libafl_targets = { version = "0.11.2", features = [
    "sancov_8bit",
    "observers",
] }