w/return results blocks client receive pipeline

[rafikiassumani-msft]

This was already an issue with Task returning .On methods, but client results likely makes it more likely to block on the client side

• .NET client blocks other .On handlers but does not block the receive loop
• JS client doesn't block anything, .On handlers for future invokes/sends can still run while blocked on user input, pings/etc. still received and processed
• Java client blocks other .On handlers but does not block the receive loop

[ghost]

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We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
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