Clamp end index for partially filled chunks

[dru1x]

Summary

RequestExceptionHandler no longer overstates PushError::endIndex for the final chunk of a batch when the total item count isn't an exact multiple of the batch size.

Changes

• RequestExceptionHandler now takes a totalCount constructor argument and clamps endIndex to min($startIndex + $batchSize, $totalCount) - 1, instead of always assuming a full-size batch.
• ExpoPush::makeRequestPool() now accepts and threads through the actual total item count: $pushMessages->notificationCount() for sendNotifications(), $receiptIds->count() for getReceipts().

Testing

Added to tests/Unit/Request/RequestExceptionHandlerTest.php:

• invoke_clamps_end_index_for_partial_final_batch — constructs the handler with a totalCount that isn't a multiple of batchSize and asserts the reported endIndex matches the actual last item index rather than a full
  batch's worth.

Added to tests/Feature/SendNotificationsTest.php and tests/Feature/GetReceiptsTest.php:

• send_notifications_reports_correct_end_index_for_partial_final_batch (950 messages, chunks of 100) and get_receipts_reports_correct_end_index_for_partial_final_batch (10,500 receipt IDs, chunks of 1000) — fail the
  final, partial chunk and assert the resulting PushError's startIndex/endIndex stay within the actual input range.

Related Issues

Fixes #89