Project reindex fails with "bulk update already running" 503 error due to concurrent Jira API property updates (Xray Cloud)

Description:

Project reindex fails on Xray Cloud with the error "Error re-indexing Xray issues - There were errors while synchronizing Jira issues with the Xray database."

The root cause is that the Jira API rejects bulk issue property updates with an HTTP 503 ("The task was rejected because another bulk update on the same issues is running") when concurrent batches overlap.

How to reproduce:

1. Navigate to Xray Project Settings and open the Re-Indexing page for any project.
2. Trigger a full project reindex.
3. Observe the reindex progress and completion screen.
4. The reindex job completes but displays: "Error re-indexing Xray issues - There were errors while synchronizing Jira issues with the Xray database. Please contact your Jira administrator."

Actual result:

Reindex fails with the generic UI error: "Error re-indexing Xray issues - There were errors while synchronizing Jira issues with the Xray database."

Expected result:

Reindex completes successfully without errors. Bulk issue property updates are processed sequentially (or with proper retry/backoff logic) so that concurrent Jira API calls do not conflict.