Add support for CRDT updates

[rjwebb]

This PR adds support for the y.js Doc CRDT to Canvas.

This is a second pass, following #439 and the earlier proof of concept at https://github.com/canvasxyz/gossiplog-yjs.

The document update type is integrated into a a new Message type, where payload.type === "updates" so we now have Message<Action | Session | Snapshot | Updates>.

Updates may include yjs Insert, yjs Delete, and yjs ApplyDelta operations. Yjs operations are applied to Yjs tables, which always have the form { id: string, [key]: "yjs-doc" }, so a document editor would have a schema like:

export const models = {
  documents: {
    id: "primary",
    content: "ytext",
  },
}

export const actions = {
  async applyDeltaToDoc(db, index, text) {
    await db.ytext.applyDelta("documents", "0", index, text)
  },
}

For the relevant code, look at packages/core/src/DocumentStore.ts and action handlers inside AbstractRuntime.

---

"Update" message type implementation

• extend MessageType with Update, which describes a message that contains a Y.js diff
• update Secp256k1DelegateSigner to expect Action | Session | Snapshot | Update
• update AbstractRuntime:
  • store yjs text docs
  • add new yjs methods (e.g. insert, delete, format on text)
  • when a yjs method is called from an append, compute the diff
  • and then append another message with the diffs
  • when a Update message is handled, update the yjs doc
• add test to show that CRDTs converge on concurrent apps
• update the yjs state when a snapshot is loaded
• add ytext column to the snapshot test

How has this been tested?

• CI tests pass
• Tested with example-chat (including login, all signers, and exchanging messages)
• Tested with @canvas-js/test-network: (optional)

Does this contain any breaking changes to external interfaces?

• Contract interfaces
• Core interface
• CLI
• Data storage formats, including IndexedDB, SQLite, or filesystem storage (will this break existing apps?)