add .size() to ArrowFile

fsspec/implementations/arrow.py

@@ -241,6 +241,10 @@ def __init__(self, fs, stream, path, mode, block_size=None, **kwargs):
     def __enter__(self):
         return self
 
+    @property
+    def size(self):
+        return self.stream.size()
+
     def __exit__(self, *args):
         return self.close()