y-prosemirror

How to write tests and fuzz tests using lib0's homegrown testing framework (`lib0/testing`, `lib0/prng`, and `lib0/schema` for random value generation). Use this skill whenever writing or modifying `*.test.js` files in this repo, adding a new test module to `src/test.js`, debugging a failing test run, or writing fuzz / property-based tests with seeded PRNGs.