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

uv.lock

@@ -217,6 +217,7 @@ dependencies = [
     { name = "opencv-python" },
     { name = "pillow" },
     { name = "pillow-avif-plugin" },
+    { name = "pyarrow" },
 ]
 
 [package.dev-dependencies]
@@ -232,6 +233,7 @@ requires-dist = [
     { name = "opencv-python", specifier = ">=4.9" },
     { name = "pillow", specifier = ">=10.4" },
     { name = "pillow-avif-plugin", specifier = ">=1.4" },
+    { name = "pyarrow", specifier = ">=17.0" },
 ]
 
 [package.metadata.requires-dev]