Add fuzzing by way of ClusterFuzzLite

[DavidKorczynski]

This adds fuzzing by way of ClusterFuzzLite, which is a GitHub action that will perform a short amount of fuzzing for new PRs. The goal is to use fuzzing to catch bugs that may be introduced by new PRs.

I added a fuzzer that targets json_walk, and currently set the timeout of CFLite to 100 seconds. CFLite will flag if the fuzzer finds any issues in the code introduced by a PR.

If you'd like to test this the way ClusterFuzzLite runs it (by way of OSS-Fuzz) you can use the steps:

git clone https://github.com/google/oss-fuzz
git clone https://github.com/DavidKorczynski/frozenfrozen
cd frozen
git checkout clusterfuzzlite

# Build the fuzzers in .clusterfuzzlite
python3 ../oss-fuzz/infra/helper.py build_fuzzers --external $PWD

# Run the fuzzer for 10 seconds
python3 ../oss-fuzz/infra/helper.py run_fuzzer --external $PWD json_walk_fuzzer -- -max_total_time=10