`cabal-validate`: "Keep going" mode

[9999years]

If any tests fail, the whole ./validate.sh script exits early. This is useful for quick feedback, but can make it annoying to get a grasp on the full set of errors when making larger refactors. I have to fix all the errors in a test suite before I can get to the next one to even see if it errors.

Proposal: There should be a --keep-going or --no-fail-fast option which continues even if a test suite fails. The exit code should still be set the same (any test failures lead to a non-zero exit code) and a summary of which steps passed or failed should be printed at the end of the output.