Fix #5213: Correct retry ack handling in DownStreamMsgContext

[nagarjunahp88-byte]

What does this PR do?

This PR fixes the retry acknowledgment handling logic in
DownStreamMsgContext to correctly handle timeout scenarios
and prevent incorrect retry behavior.

What was the problem?

The existing logic could incorrectly retry or acknowledge
messages even after the configured TTL was exceeded, leading
to unexpected message handling behavior.

How was it fixed?

• Corrected the retry ack decision logic based on elapsed time
• Ensured retries are discarded once TTL is exceeded
• Added unit tests to validate retry ack timeout scenarios

Tests

• Added unit tests for retry acknowledgment behavior

Fixes #5213

[github-actions]

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