Add license header to py_nvbench.cpp

Also updated comment as to why calling
`nvbench::benchmark_manager::get().initialize()` is necessary
for running all tests.

Author: oleksandr-pavlyk

python/src/py_nvbench.cpp

@@ -1,4 +1,20 @@
-// TODO: Copyright header
+/*
+ *  Copyright 2025 NVIDIA Corporation
+ *
+ *  Licensed under the Apache License, Version 2.0 with the LLVM exception
+ *  (the "License"); you may not use this file except in compliance with
+ *  the License.
+ *
+ *  You may obtain a copy of the License at
+ *
+ *      http://llvm.org/foundation/relicensing/LICENSE.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
 
 #include <nvbench/nvbench.cuh>
 
@@ -140,8 +156,8 @@ class GlobalBenchmarkRegistry
 
     try
     {
-      // TODO: This line is mandatory for correctness
-      //    Q: Why is initializing at module init not enough?
+      // This line is mandatory for correctness to populate
+      // benchmark with devices requested by user via CLI
       nvbench::benchmark_manager::get().initialize();
       {
         nvbench::option_parser parser{};
@@ -184,6 +200,8 @@ PYBIND11_MODULE(_nvbench, m)
 
   NVBENCH_DRIVER_API_CALL(cuInit(0));
 
+  // This line ensures that benchmark_manager has been created during module init
+  // It is reinitialized before running all benchmarks to set devices to use
   nvbench::benchmark_manager::get().initialize();
 
   // TODO: Use cuModuleGetLoadingMode(&mode) to confirm that (mode == CU_MODULE_EAGER_LOADING)