Optimize lesson report for large data sets

The lesson report overview would not complete in a course with a large number of users. The problem course has around 14,000 users and 60,000 attempts for the given lesson. The report would complete if given enough time. I removed the limits and had it complete in around 15 minutes. The report winds up outputting around 27,000 rows of user attempts.

With some optimizations I got the report to finish in less than 30 seconds.
I was able to remove the use DISTINCT in the reports SQL. I fetch both the users and attempts at once using a JOIN and a GROUP BY.

The lesson tools data structure is not good but that's a whole other issue.