fix typing

Author: patricktnast

setup.py

@@ -59,6 +59,7 @@
         "vivarium_dependencies[lint]",
         "types-setuptools",
         "types-psutil",
+        "pyarrow-stubs",
     ]
 
     test_requirements = [

src/vivarium_cluster_tools/psimulate/results/processing.py

@@ -113,7 +113,7 @@ def bytes_per_row(self, metric: str) -> float:
         """
         chunk_0_path = self.results_dir / metric / "chunk_0000.parquet"
         if chunk_0_path.exists():
-            rows = pq.read_metadata(chunk_0_path).num_rows
+            rows: int = pq.read_metadata(chunk_0_path).num_rows
             if rows > 0:
                 return chunk_0_path.stat().st_size / rows
         return DEFAULT_BYTES_PER_ROW_ESTIMATE