With this chunking strategy, the runtimes of tests are taken into account, such that each chunk
takes roughly the same amount of time to finish. Tests belonging to the same manifest will not get
split up.
The algorithm works by sorting every manifest from slowest to fastest. Each manifest is popped off
and its tests are added to the fastest chunk to date until no manifests are left. Total runtimes of
the chunks are re-calculated after every addition.
