feat: Add async iterable support for paginating query results

[anatolzak]

closes #563

Summary

• Introduces AsyncIterable support on .go() for query, scan, and collection operations, enabling for await...of iteration over pages of DynamoDB results
• Each iteration yields a single page with its own { data, cursor }, allowing streaming processing, early termination via break, and lower memory usage for large result sets
• Fully backward-compatible — .go() still works as a Promise via .then()/await; async iteration is opt-in
• important: .go() execution is now lazy — the request to DynamoDB is deferred until the result is consumed via await, .then(), or for await...of

How it works

A new ElectroQueryResult class wraps query execution. It implements both PromiseLike (so await entity.query.go() works exactly as before) and AsyncIterable (so for await (const page of entity.query.go()) yields individual pages). Internally, executeQuery was refactored from collecting all pages into a single array to an async generator that yields each page as it arrives from DynamoDB.

Example

for await (const page of MallStores.query.leases({ mallId }).go({ pages: "all" })) {
  console.log(page.data);   // items for this page
  console.log(page.cursor);  // cursor for this page
  if (done) break;           // stop pagination early
}

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