add concatenate_traces to utils
add concatenate_traces to utils


Former-commit-id: 2891c563a4c723c655afc325b798ff649093115f [formerly 19a90e209cb8ea87b8bbc328cbdd709530e2ff38] [formerly 87ca88ef9a843c8350fa07746b2d69ffa234ac20]
Former-commit-id: 4176f6e3b89c806c33909a234835e8a73d450d66
Former-commit-id: 4daf28df26e5d194ebb32d9090cb17c3a0cc1b49
dssg/wikienergy,dssg/wikienergy,dssg/wikienergy,dssg/wikienergy,dssg/wikienergy