Revamp the rabit implementation. (#10112)

This PR replaces the original RABIT implementation with a new one, which has already been partially merged into XGBoost. The new one features:
- Federated learning for both CPU and GPU.
- NCCL.
- More data types.
- A unified interface for all the underlying implementations.
- Improved timeout handling for both tracker and workers.
- Exhausted tests with metrics (fixed a couple of bugs along the way).
- A reusable tracker for Python and JVM packages.

src/logging.cc

@@ -1,14 +1,13 @@
-/*!
- * Copyright 2015-2018 by Contributors
+/**
+ * Copyright 2015-2024, XGBoost Contributors
  * \file logging.cc
  * \brief Implementation of loggers.
  * \author Tianqi Chen
  */
-#include <iostream>
-
-#include "xgboost/parameter.h"
 #include "xgboost/logging.h"
 
+#include <string>  // for string
+
 #include "collective/communicator-inl.h"
 
 #if !defined(XGBOOST_STRICT_R_MODE) || XGBOOST_STRICT_R_MODE == 0