All errors should be declared in p2p_errors.ml ? Follow-up from "p2p_io_scheduler: test read* functions"

The following discussion from !3194 (merged) should be addressed:

• @vivienpe started a discussion: (+1 comment)

  Usually, errors are declared in the file src/lib_p2p_services/p2p_errors.ml.
  Is there a specific motive to declare this error here ?