Add failure-exit-code option to customize exit code on test failures

[hatsu38]

Feature Request

I would like to propose the addition of a failure-exit-code option, similar to what is available in RSpec. This option would allow users to specify the exit code that the test suite should return upon failing tests.

Use Case

The main motivation for this feature is to allow the test suite to exit with a code of 0 even when some tests fail. This can be particularly useful in certain CI environments where a non-zero exit code typically indicates a more severe problem than test failures, or where the build should proceed regardless of test results.