- Add nil service guards to Register/Deregister/Renew in gRPC and HTTP
plugins to prevent nil pointer dereferences
- Remove unused log field from grpcPlugin and httpPlugin
- Prefix HTTP error messages with operation context (sd register/deregister/renew/get)
- Return gRPC Register error directly instead of logging + returning
- Add 33 unit tests covering all operations, nil guards, and error paths
- Add 808-line loader_test.go covering registerGroup, register, and Load
- Add package and exported symbol doc comments to loader.go
- Fix fmt.Errorf(resp.Status) → errors.New(resp.Status) in sd/plugin/http.go
(resp.Status is a plain string, not a format string)
ginuerzh