2022 12 21 fuzz

[thedavidmeister]

sibling PR to https://github.com/holochain/holochain-serialization/pull/42 and instructions are largely the same

e.g. try

docker run --env FUZZ_TARGET=round_trip_u64 --rm -it holochain/fuzzbox:holochain-wasmer

after running the fuzzprep.sh from https://github.com/holochain/fuzzbox

• builds fuzzbox docker on CI
• adds some fuzz tests that can be run
• makes wasmer guest support usize so that the fuzz tests pass
• updates niv