Fix ruff B008: use module-level singleton for default ScanOrder

Replace TaskOrder() function call in argument default with a
module-level singleton _DEFAULT_SCAN_ORDER to satisfy ruff B008
(no function calls in argument defaults).

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

Author: sumedhsakdeo

pyiceberg/io/pyarrow.py

@@ -1755,6 +1755,9 @@ def worker(task: FileScanTask) -> None:
                     break
 
 
+_DEFAULT_SCAN_ORDER: ScanOrder = TaskOrder()
+
+
 class ArrowScan:
     _table_metadata: TableMetadata
     _io: FileIO
@@ -1837,7 +1840,7 @@ def to_table(self, tasks: Iterable[FileScanTask]) -> pa.Table:
     def to_record_batches(
         self,
         tasks: Iterable[FileScanTask],
-        order: ScanOrder = TaskOrder(),
+        order: ScanOrder = _DEFAULT_SCAN_ORDER,
     ) -> Iterator[pa.RecordBatch]:
         """Scan the Iceberg table and return an Iterator[pa.RecordBatch].