[CometFuzz] Show summary of test coverage

[andygrove]

What is the problem the feature request solves?

We currently have no visibility into which expressions were successfully tested after running generated queries. It is possible that all queries for a particular expression may have failed both in Spark and Comet because the query was not valid.

Describe the potential solution

Generate a markdown or HTML report summarizing the coverage for each expression

Additional context

No response

[andygrove]

This could also test whether each expression was actually accelerated by Comet or fell back to Spark