switch transaction queue completion to a new ValuedEvent

[altendky]

Purpose:

#17171 was the introducing pr.
it seems this error would have been triggered when the api handler timed out waiting for the transaction to be processed and the transaction processing later completed. i didn't feel great about using the future there and ended up getting bit by it. when awaiting a future gets cancelled it marks the future itself as cancelled. when something later attempts to set a result on it the invalid state error is raised. in this case, i believe the only effect of this bug is the logging of the error.

Current Behavior:

New Behavior:

Testing Notes:

[coveralls-official]

Pull Request Test Coverage Report for Build 7503678079

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 90.484%

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Totals
Change from base Build 7497287764:	-0.05%
Covered Lines:	94583
Relevant Lines:	104480

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💛 - Coveralls