* Pin range scope vars
* Don't disable scopelint
This PR repairs linter errors seen when running the following commands:
golangci-lint run --no-config --disable-all=true --enable=scopelint
Contributes to #3262
* Fix random distribution in bitArray.PickRandom
Previously it was very biased. 63 "_" followed by a single "x" had
much greater odds of being chosen. Additionally, the last element was
skewed. This fixes that by first preproccessing the set of all true
indices, and then randomly selecting a single element from there.
This commit also makes the code here significantly simpler, and
improves test cases.
* unlock mtx right after we select true indices
