This also requires doing something to keep the TxGroup in each Qcx
from holding its Tx references after the Qcx closes, because otherwise
the list of Qcxs that we keep to verify that they all got closed ends
up keeping every shared/read-only Tx open forever, resulting in many
gigabytes of memory usage when running with the race detector. To
avoid having to reason about whether anything would ever access a nil
TxGroup, or run through iteratively zeroing maps, we just make a new
empty group at that point.
In [SUP-75](https://molecula.atlassian.net/browse/SUP-75?atlOrigin=eyJpIjoiYmU5MzdkMmUyZTAyNGQ2Y2IzMDMzYTgzMDU2Y2ZhNmMiLCJwIjoiaiJ9) Allen
pointed out that the time estimation is really good for the first couple lines of output, but gets exponentially worse as execution continues.
After looking into it, it looks like we’re currently using a heuristic based on the amount of messages processed in the previous
second(ish) which is what results in that sort of exponential drop off.
To remedy this, I adjusted the time estimation calculation to use the average time per message up to the point of calculating the new
estimate to ideally improve estimates over time, with the trade-off of a potentially less accurate estimate to begin with.