feat: implement an exponential-backoff to find echo message

[medtaher123]

This PR introduces exponential backoff when checking for existing messages to prevent duplicate echo messages. Previously, echo messages could arrive before the original message was saved, causing them to be incorrectly treated as new messages.

Changes:

• Implemented retry logic with exponential backoff in findMessageWithRetries().
• Instead of immediately assuming an echo message is new, the system retries checking for its existence with increasing delay.

Behavior:

1. When an echo message arrives, the system checks if the message exists.
2. If not found, it waits and retries multiple times (default: 5 attempts, doubling the delay each time).
3. If still not found after all retries, it is treated as an external echo.

serves Issue #746