Support Millisecond Precision for sentAt and updatedAt Timestamps

Currently, CometChat provides sentAt and updatedAt fields as Unix timestamps in seconds (10-digit format). This limitation can lead to inconsistent or non-deterministic ordering when multiple messages are sent within the same second, especially in high-frequency messaging scenarios.

While using the auto-incrementing id field as a secondary sort key serves as a workaround, it introduces additional client-side logic and does not fully replace the need for precise timestamping.