add pyarrow as an explicit dependency

The bbox input path and the tests import pyarrow directly; it was
present only because dora-rs pulls it in transitively.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JPUZks9z3Pi5oxw9GQ9znt

pyproject.toml

@@ -17,6 +17,7 @@ dependencies = [
   "opencv-python >= 4.9",
   "pillow >= 10.4",
   "pillow-avif-plugin >= 1.4",
+  "pyarrow >= 17.0",
 ]
 
 [project.scripts]