SCORU/Node: move injector instantiation outside of proto directory
Context
This MR moves the instantiation of the injector outside of the proto_* directories. Each protocol specific rollup node code registers their own "proto client" to the injector in order for the latter to support the protocol.
Depends on !8625 (merged) and !8824 (merged).
Manually testing the MR
Refactoring, CI.