In insert_many, we discard any partial results we've accumulated when we return BulkWriteFailures, since it is optional to report them per the crud spec. It may be surprising to users that their operation reported as failing when in fact it was mostly successful (imagine a large batch where there was a single write error).

We should consider reporting these partial results to users, so that even in the event an error is encountered, they can see how their data was modified.