tests: Add fuzzing harness for CScript and CScriptNum operations
Summary:
Add fuzzing harness for CScript and CScriptNum operations.
Backport of core PR18176.
Test Plan:
ninja bitcoin-fuzzers ./test/fuzz/test_runner.py <path_to_corpus>
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D8959