test(detectors): add detector-to-detector communication via writable datastores

Add comprehensive test validating core use case where detectors share data
through writable datastores. Tests proper event-based communication where
one detector writes threat intelligence and another reads it during event
processing.

Test scenarios:
- Threat intelligence sharing between detectors
- Ownership model (single writer, multiple readers)
- Graceful degradation when store unavailable
- Batch operations (1000+ entries)

All communication happens through OnEvent() methods, demonstrating realistic
detector interaction patterns.

Author: yanivagman