fix: close OAuth popup from parent (#973)

On iOS, a browser window can't close itself via `window.close()`:
instead, it must be closed by the same context that called `window.open`
to open it. This means that for iOS we cannot rely on the OAuth callback
window to close itself in the popup-based flow. Instead, we'll have the
parent close it upon receiving a message.

account-kit/signer/src/client/index.ts

@@ -454,6 +454,7 @@ export class AlchemySignerWebClient extends BaseSignerClient<ExportWalletParams>
         const { alchemyBundle: bundle, alchemyOrgId: orgId } = event.data;
         if (bundle && orgId) {
           cleanup();
+          popup?.close();
           this.completeAuthWithBundle({
             bundle,
             orgId,