tests: Add fuzzing harnesses for functions/classes in chain.h and protocol.h

Summary:

Add fuzzing harnesses for functions/classes in chain.h and protocol.h.

Backport of core PR18445.

Adapted to match our codebase.

Test Plan:

ninja bitcoin-fuzzers
./test/fuzz/test_runner.py <path_to_corpus>

Reviewers: #bitcoin_abc, PiRK, majcosta

Reviewed By: #bitcoin_abc, PiRK, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8979