feat: add ingestBatch method to datasource accessors

[gnzjgo]

Closes #132

Adds ingestBatch(events, options?) to the DatasourceAccessor type and runtime implementation, so users can do:

await tinybird.myDatasource.ingestBatch([
  { id: '1', name: 'Alice' },
  { id: '2', name: 'Bob' },
]);

The underlying client.ingestBatch() already existed — this just wires it into the generated typed accessors.