[Misc] Add SPDX-License-Identifier headers to python source files (#12628)

- **Add SPDX license headers to python source files**
- **Check for SPDX headers using pre-commit**

commit 9d7ef44c3cfb72ca4c32e1c677d99259d10d4745
Author: Russell Bryant <rbryant@redhat.com>
Date:   Fri Jan 31 14:18:24 2025 -0500

    Add SPDX license headers to python source files
    
This commit adds SPDX license headers to python source files as
recommended to
the project by the Linux Foundation. These headers provide a concise way
that is
both human and machine readable for communicating license information
for each
source file. It helps avoid any ambiguity about the license of the code
and can
    also be easily used by tools to help manage license compliance.
    
The Linux Foundation runs license scans against the codebase to help
ensure
    we are in compliance with the licenses of the code we use, including
dependencies. Having these headers in place helps that tool do its job.
    
    More information can be found on the SPDX site:
    
    - https://spdx.dev/learn/handling-license-info/

Signed-off-by: Russell Bryant <rbryant@redhat.com>

commit 5a1cf1cb3b80759131c73f6a9dddebccac039dea
Author: Russell Bryant <rbryant@redhat.com>
Date:   Fri Jan 31 14:36:32 2025 -0500

    Check for SPDX headers using pre-commit
Signed-off-by: Russell Bryant <rbryant@redhat.com>

---------
Signed-off-by: Russell Bryant <rbryant@redhat.com>

tests/distributed/test_ca_buffer_sharing.py

+# SPDX-License-Identifier: Apache-2.0
+
 # can only run on machines with p2p access across GPUs
 # can only run with torchrun:
 # torchrun --nproc_per_node=2 tests/distributed/test_ca_buffer_sharing.py

tests/distributed/test_comm_ops.py

+# SPDX-License-Identifier: Apache-2.0
 """Test the communication operators.
 
 Run `pytest tests/distributed/test_comm_ops.py`.

tests/distributed/test_custom_all_reduce.py

+# SPDX-License-Identifier: Apache-2.0
+
 import os
 import random
 

tests/distributed/test_distributed_oot.py

+# SPDX-License-Identifier: Apache-2.0
+
 from ..entrypoints.openai.test_oot_registration import (
     run_and_test_dummy_opt_api_server)
 

tests/distributed/test_multi_node_assignment.py

+# SPDX-License-Identifier: Apache-2.0
 """Make sure ray assigns GPU workers to the correct node.
 
 Run:

tests/distributed/test_pipeline_parallel.py

+# SPDX-License-Identifier: Apache-2.0
 """
 WARNING: This test runs in both single-node (4 GPUs) and multi-node
  (2 node with 2 GPUs each) modes. If the test only uses 2 GPUs, it is

tests/distributed/test_pipeline_partition.py

+# SPDX-License-Identifier: Apache-2.0
+
 import os
 
 import pytest

tests/distributed/test_pp_cudagraph.py

+# SPDX-License-Identifier: Apache-2.0
+
 import os
 
 import pytest

tests/distributed/test_pynccl.py

+# SPDX-License-Identifier: Apache-2.0
+
 import multiprocessing
 import os
 from typing import Dict, List

tests/distributed/test_same_node.py

+# SPDX-License-Identifier: Apache-2.0
+
 import os
 
 import torch.distributed as dist

tests/distributed/test_shm_broadcast.py

+# SPDX-License-Identifier: Apache-2.0
+
 import multiprocessing
 import random
 import time

tests/distributed/test_torchrun_example.py

+# SPDX-License-Identifier: Apache-2.0
+
 # unit test for `examples/offline_inference/torchrun_example.py`
 
 import random

tests/distributed/test_utils.py

+# SPDX-License-Identifier: Apache-2.0
+
 import socket
 
 import pytest

tests/encoder_decoder/test_e2e_correctness.py

+# SPDX-License-Identifier: Apache-2.0
 """E2E tests to verify the correctness of the encoder-decoder framework
 
 Run `pytest tests/encoder_decoder/test_e2e_correctness.py`.

tests/engine/output_processor/test_multi_step.py

+# SPDX-License-Identifier: Apache-2.0
+
 import random
 from unittest.mock import MagicMock
 

tests/engine/output_processor/test_stop_checker.py

+# SPDX-License-Identifier: Apache-2.0
+
 from unittest.mock import MagicMock
 
 import pytest

tests/engine/test_arg_utils.py

+# SPDX-License-Identifier: Apache-2.0
+
 from argparse import ArgumentTypeError
 
 import pytest

tests/engine/test_computed_prefix_blocks.py

+# SPDX-License-Identifier: Apache-2.0
+
 import pytest
 
 from vllm.engine.arg_utils import EngineArgs

tests/engine/test_custom_executor.py

+# SPDX-License-Identifier: Apache-2.0
+
 import asyncio
 import os
 from typing import Any, Callable, Dict, List, Optional, Tuple, Union

tests/engine/test_detokenization.py

+# SPDX-License-Identifier: Apache-2.0
+
 import pytest
 
 from vllm.entrypoints.llm import LLM