Revert default Syzygy max_fds to 128

Python's mmap.mmap() actually (unnecessarily, with regard to our use
case) duplicates the file descriptor and keeps a copy around for the
lifetime of the memory map.

chess/syzygy.py

@@ -1483,7 +1483,7 @@ class Tablebase:
     """
     Manages a collection of tablebase files for probing.
     """
-    def __init__(self, *, max_fds: Optional[int] = None, VariantBoard: Type[chess.Board] = chess.Board) -> None:
+    def __init__(self, *, max_fds: Optional[int] = 128, VariantBoard: Type[chess.Board] = chess.Board) -> None:
         self.variant = VariantBoard
 
         self.max_fds = max_fds
@@ -1963,7 +1963,7 @@ def __exit__(self, exc_type: Optional[Type[BaseException]], exc_value: Optional[
         self.close()
 
 
-def open_tablebase(directory: str, *, load_wdl: bool = True, load_dtz: bool = True, max_fds: Optional[int] = None, VariantBoard: Type[chess.Board] = chess.Board) -> Tablebase:
+def open_tablebase(directory: str, *, load_wdl: bool = True, load_dtz: bool = True, max_fds: Optional[int] = 128, VariantBoard: Type[chess.Board] = chess.Board) -> Tablebase:
     """
     Opens a collection of tables for probing. See
     :class:`~chess.syzygy.Tablebase`.