Replace List-container parameters with streaming

[L-Lavigne]

The RPC service definitions in https://github.com/47deg/metrifier/blob/40dd4ec406cbbd7ef1fae911e343530e3030831f/frees-rpc/src/main/scala/service.scala are unary calls with messages that are containers for Lists. They're currently broken as per higherkindness/mu-scala#285, but independently of fixing that, we also replace them with modern streaming implementations that will better showcase freestyle-rpc features and performance.