tests: Add basic fuzzing harness for CNetAddr/CService/CSubNet related functions (netaddress.h)

Summary: Backport of core PR18047.

Test Plan:

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

Reviewers: #bitcoin_abc, PiRK

Reviewed By: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8270