bevy_ecs fuzzing

[mockersf]

Objective

• Fuzz bevy_ecs
• No bug found! 🎉

Solution

• use https://github.com/rust-fuzz/cargo-fuzz
• add fuzz targets for the command queue, hierarchy, schedule building, observers, messages, spawning/despawning entities and queries

Testing

• CI should run the fuzz tests
• for f in fuzz_targets/*.rs; do; cargo +nightly fuzz run $(basename "$f" .rs) -- -runs=1000; done

[mockersf]

#23635

[alice-i-cecile]

Yay! This is long overdue. Tests and setup both look fine to me.