feat: find id spans between

[zxch3n]

Now you can now inspect all the changes that happened in an event:

const docA = new LoroDoc();
docA.setPeerId("1");
const docB = new LoroDoc();

docA.getText("text").update("Hello");
docA.commit();
const snapshot = docA.export({ mode: "snapshot" });
let done = false;
docB.subscribe(e => {
  const spans = docB.findIdSpansBetween(e.from, e.to);
  expect(spans.retreat).toHaveLength(0);
  expect(spans.forward).toHaveLength(1);
  expect(spans.forward[0]).toEqual({
    peer: "1",
    counter: 0,
    length: 5,
  });
  const changes = docB.exportJsonInIdSpan(spans.forward[0]);
  expect(changes).toStrictEqual([{
    id: "0@1",
    timestamp: expect.any(Number),
    deps: [],
    lamport: 0,
    msg: undefined,
    ops: [{
      container: "cid:root-text:Text",
      counter: 0,
      content: {
        type: "insert",
        pos: 0,
        text: "Hello"
      }
    }]
  }]);
  done = true;
});
docB.import(snapshot);
await Promise.resolve();
expect(done).toBe(true);