Test mode

[nolanlawson]

I can imagine people wanting to use fuite in their CI tests to exit with a 0 or a 1 based on whether any leaks were detected. The CLI could do this today, but it'd be a breaking change because currently it's always 0 unless an unexpected error occurs.

There would probably need to be a system to help manage false positives, e.g. --maxAllowedLeakingCollections or --maxAllowedLeakingObjects. It could either be a superset of the existing CLI, or a new CLI (e.g. fuite-test).

Or it could be a separate standalone tool. Or something that could be integrated into a test runner. Or maybe just some documentation about how to run the existing tool and output the exit code you want. I dunno.