First Failing Build
`builds` is a CI build history, represented as a list of booleans: some run of True (passing builds) followed by a run of False (failing builds) — never the other way around. Find the index of the first failing build. If every build passed, return -1.
`builds` is a CI build history, represented as a list of booleans: some run of True (passing builds) followed by a run of False (failing builds) — never the other way around. Find the index of the first failing build. If every build passed, return -1.
