Fix: prevent cron worker OOM by batching recurring check-in and creation operations

[Ganeshswaminathan1912]

Fixes #1872

What changes did you make and why did you make them ?

Summary of changes

• Removed implicit type coercion by switching time comparisons to numeric timestamps instead of UTC strings, fixing incorrect event timing and cases where events did not open for check-in.
• Added guards for invalid date values and improved error handling to prevent worker crashes.
• Replaced per-event creation loops with insertMany for recurring event creation to reduce request volume and memory usage, preventing cron worker from crashing.
• Added a new API route using bulkWrite for batch PATCH updates (open/close check-ins), while preserving the existing single-event endpoint to avoid breaking dependent services.
• Emulated the ECS production environment locally with equivalent resources and verified correct behavior through logs (smooth create → open → close flow).
• Updated unit tests in createRecurringEvents.test.js for batch POST request to test the updated code.

No UI changes. Backend-only cron and API updates. Logs attached
cron-run.log

Screenshots of Proposed Changes Of The Website (if any, please do not screen shot code changes)

Visuals before changes are applied

Visuals after changes are applied

[trillium]

Clean refactor that fixes OOM by batching API calls. N events now = 1 API call instead of N individual calls. Well-documented with JSDoc, tests updated, backward compatible. LGTM.