Add consumer errors and clean up consumer code

[milindl]

Contains changes and error handling for the consumer.

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We might need to take a deeper dive into seeing how auto-commit is handled, as well as multiple eachMessage's dispatched at once. Both of them are fairly critical features, and we have large semantic differences.

But I'll handle that in another PR, it needs some significant discussion.

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✅ milindl
❌ emasab
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