Listing generated mutants

--list: Show what mutants could be generated, without running them.

--diff: With --list, also include a diff of the source change for each mutant.

--json: With --list, show the list in json for easier processing by other programs. (The same format is written to mutants.out/mutants.json when running tests.)

--check: Run cargo check on all generated mutants to find out which ones are viable, but don't actually run the tests. (This is primarily useful when debugging cargo-mutants.)