Cleanup; Separated declaration and implementation of [Node]DataTransfer methods

4 jobs for feature/data_transfer_implementation in 32 minutes and 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #8432
debian:10 clang-6-libcpp-17

00:32:57

passed #8431
debian:10 gcc-8-17

00:21:34

passed #8433
debian:9 gcc-6-14

00:23:09

passed #8434
ubuntu:18.04 clang-6-17

00:30:20