Fuzzing setup

ref-fvm uses ClusterFuzzLite for contious fuzzing. This consists of four workflows:

• cflite_pr.yml - responsible for running fuzzing for PRs, it will only fuzz targets when diff affects files covered by given fuzzing target
• cflite_build.yml - responsible for building fuzzing targets on master branch and storing them for recall. These recalled targets are used to detect if crasher is a new thing caused by changes or a newely discovered input which will also cause crash on master.
• cflite_batch.yml - periodically (every 6h for 1h) runs fuzzing to develop the corpus which will be used for other on-demand fuzzing and as seed corpus for OSS-Fuzz.
• cflite_cron.yml - every day generates coverage reports, as well as, prunes and mimizes the corpus.

Corpus and coverage data is stored within https://github.com/filecoin-project/ref-fvm-fuzz-corpora