start removal of six and improve type annotation (#607)

* fix unfinished Python2 -> 3 translation
* remove some six usage
* annotate
* fix regression in Six removal
* mypy: self.enf is always defined
* fix return type of cups.py
* Usb idVendor/idProduct are integers
* self.default_args is always defined
* tweak usb_args, PEP589 is better
* lp.py: reassure mypy
* correctly cast call to CashDrawerError()
* update CUPS test
* add missing close() method in metaclass
* document a bug in typeshed
* query_status() returns bytes as seen in constants.py
* remove more SIX usage
* test examples too
* remove type comment where type is annotated
* adapt behavior of cups printer to match other implementations

---------

Co-authored-by: Patrick Kanzler <dev@pkanzler.de>
Co-authored-by: Patrick Kanzler <4189642+patkan@users.noreply.github.com>

src/escpos/printer/lp.py

@@ -182,12 +182,13 @@ class LP(Escpos):
         if not self._is_closing:
             self.open(_close_opened=False)
 
-    def _raw(self, msg):
+    def _raw(self, msg: bytes) -> None:
         """Write raw command(s) to the printer.
 
         :param msg: arbitrary code to be printed
-        :type msg: bytes
         """
+        assert self.device is not None
+        assert self.device.stdin is not None
         if self.device.stdin.writable():
             self.device.stdin.write(msg)
         else: