Switch lighton-ocr2.py to stable vLLM (>=0.15.1), drop nightly index

LightOnOCR-2 architecture is in stable vLLM since 0.15.1.
Also bumps datasets>=4.0.0 and drops pyarrow<18 pin.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lighton-ocr2.py

@@ -1,21 +1,14 @@
 # /// script
 # requires-python = ">=3.11"
 # dependencies = [
-#     "datasets>=3.1.0",
-#     "pyarrow>=17.0.0,<18.0.0",
+#     "datasets>=4.0.0",
 #     "huggingface-hub",
 #     "pillow",
-#     "vllm",
+#     "vllm>=0.15.1",
 #     "tqdm",
 #     "toolz",
 #     "torch",
 # ]
-#
-# [[tool.uv.index]]
-# url = "https://wheels.vllm.ai/nightly/cu129"
-#
-# [tool.uv]
-# prerelease = "allow"
 # ///
 
 """