add missing close() method in metaclass

src/escpos/escpos.py

@@ -154,6 +154,10 @@ class Escpos(object, metaclass=ABCMeta):
         """Open a printer device/connection."""
         pass
 
+    def close(self):
+        """Close a printer device/connection."""
+        pass
+
     @abstractmethod
     def _raw(self, msg: bytes) -> None:
         """Send raw data to the printer.

test/test_printers/test_printer_cups.py

@@ -173,4 +173,4 @@ def test_read_no_device(cupsprinter) -> None:
     THEN check the return value is b''
     """
     cupsprinter.device = None
-    assert cupsprinter._read() == b''
+    assert cupsprinter._read() == b""