Feat: Improve Fuzz test coverage

[alexanderwiederin]

A couple resources about fuzzing with dictionaries:

• Demo in libFuzzer tutorial: https://github.com/google/fuzzing/blob/master/tutorial/libFuzzerTutorial.md#dictionaries
• libFuzzer documentation: https://llvm.org/docs/LibFuzzer.html#dictionaries
• Example dictionaries: https://github.com/google/fuzzing/tree/master/dictionaries

Some state machine fuzz targets that have found important bugs in LDK over the years (might be helpful or provide inspiration):

• https://github.com/lightningdevkit/rust-lightning/blob/main/fuzz/src/chanmon_consistency.rs
• https://github.com/lightningdevkit/rust-lightning/blob/main/fuzz/src/full_stack.rs

Continuous fuzzing vs. manual periodic fuzzing:
LDK provides a good case study here. They do manual fuzzing before releases, which is good. However, continuous fuzzing in the cloud discovered lightningdevkit/rust-lightning#4139 (comment) much earlier than it would have been found through periodic manual fuzzing alone.

Credits for pointers: Matt Morehouse