Move ucxx::Request status setting to base class

Setting the status from a derived class before `callback()`, and,
therefore `setStatus()`, can be dangerous in situations where the user
code is not holding a reference to the request. In such cases, the user
code may be checking for the status to change to immediately continue by
releasing the request, when that happens and `setStatus()` is eventually
called, that will be operating on an invalid `ucxx::Request` object.

cpp/src/request.cpp

@@ -162,20 +162,14 @@ void Request::setStatus(ucs_status_t status)
   if (_endpoint != nullptr) _endpoint->removeInflightRequest(this);
   _worker->removeInflightRequest(this);
 
-  if (_status == UCS_INPROGRESS) {
-    // If the status is not `UCS_INPROGRESS`, the derived class has already set the
-    // status, a truncated message for example.
-    _status.store(status);
-  }
-
-  ucs_status_t s = _status;
-
   ucxx_trace_req_f(_ownerString.c_str(),
                    _request,
                    _operationName.c_str(),
                    "callback called with status %d (%s)",
-                   s,
-                   ucs_status_string(s));
+                   status,
+                   ucs_status_string(status));
+
+  _status.store(status);
 
   if (_enablePythonFuture) {
     auto future = std::static_pointer_cast<ucxx::Future>(_future);

cpp/src/request_stream.cpp

@@ -92,8 +92,7 @@ void RequestStream::populateDelayedSubmission()
 
 void RequestStream::callback(void* request, ucs_status_t status, size_t length)
 {
-  status  = length == _length ? status : UCS_ERR_MESSAGE_TRUNCATED;
-  _status = status;
+  status = length == _length ? status : UCS_ERR_MESSAGE_TRUNCATED;
 
   if (status == UCS_ERR_MESSAGE_TRUNCATED) {
     const char* fmt = "length mismatch: %llu (got) != %llu (expected)";

cpp/src/request_tag.cpp

@@ -70,8 +70,6 @@ void RequestTag::callback(void* request, ucs_status_t status, const ucp_tag_recv
     std::snprintf(_status_msg.data(), _status_msg.size(), fmt, info->length, _length);
   }
 
-  _status = status;
-
   Request::callback(request, status);
 }