The previous version was showing the microseconds unit when it was
outputting nanoseconds. Now we correctly identify which sub-second unit
to use (milliseconds, microseconds, or nanoseconds) and use the correct
unit while dividing the duration unit correctly to produce the correct
output.
Also updated to use the default duration string instead of our own
custom formatters. It turns out that the string method for
`time.Duration` does the correct thing as long as we truncate the value
first.
When a limit is exceeded, we return errors and sometimes log (if appropriate)
that a limit was exceeded. The messages don't always provide an indication
as to where or how they are configured.
Instead, return the config option (easily searchable for) as well as the limit
currently set and the value that exceeded it when possible.
The task manager now acts as its own statement executor so that a custom
statement executor can perform custom actions for KillQueryStatement and
ShowQueriesStatement.