Section on structured fuzzing

[maxammann]

TLV encodings can represent a challenge to fuzzers. The idea is to choose a more structured fuzzing approach by using custom mutators that don't destroy expected boundaries/file formats like https://chromium.googlesource.com/chromium/src/+/main/testing/libfuzzer/libprotobuf-mutator.md

A lightweight workaround for this issue is FuzzedDataProvider

Motivation arises from test-fuzz partially which fuzzes TLV encoded data: trailofbits/test-fuzz#304