fix: updated span kind to CLIENT for ack and modack rpc spans

[bizob2828]

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Fixes #2028 🦕

This PR updates the span kind based on the unary pull example to set span kind to client for modack/ack spans. I also added some missing assertions from #2019

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[feywind]

@bizob2828 Thanks for the PR! Let me run this by my OTel collaborator here.

[feywind]

@bizob2828 Hey would you mind running npm run fix in your branch? We can't do that through a bot anymore :S