Fix the subscribers func type, fix method func type

It's really awfull to write this kind of suff.
It seems to be Ok right now. I hope I will not change it until long
time.

libs/lib/xaal/lib/core.py

@@ -22,7 +22,7 @@ import inspect
 import logging
 import time
 import typing
-from typing import Any, Awaitable, Optional, List, Callable, Union, TypeVar
+from typing import Any, Awaitable, Optional, List, Callable, TypeVar
 
 from .exceptions import EngineError, XAALError
 from .messages import ALIVE_ADDR, MessageAction, MessageFactory, MessageType
@@ -31,8 +31,16 @@ if typing.TYPE_CHECKING:
     from .devices import Device, Attribute
     from .messages import Message
 
-
+# Function type w/ no argument, and no return (Timer, Hooks)
 FuncT = TypeVar("FuncT", Callable[[], None], Callable[[], Awaitable[None]])
+
+# Function type w/ message as argument (subscribers), no return
+SubFuncT = TypeVar(
+        "SubFuncT",
+        Callable[[str], None],
+        Callable[[str], Awaitable[None]]
+)
+
 logger = logging.getLogger(__name__)
 
 
@@ -199,11 +207,11 @@ class EngineMixin(object):
     #####################################################
     # xAAL messages subscribers
     #####################################################
-    def subscribe(self, func: Any):
+    def subscribe(self, func: SubFuncT):
         # func should be a Callable[[Message],None], but it can be a coroutine too
         self.subscribers.append(func)
 
-    def unsubscribe(self, func: Any):
+    def unsubscribe(self, func: SubFuncT):
         self.subscribers.remove(func)
 
     #####################################################

libs/lib/xaal/lib/devices.py

@@ -21,7 +21,7 @@
 import logging
 import time
 import typing
-from typing import Any, Optional, Union, Callable
+from typing import Any, Optional, Union, Callable, TypeVar, Awaitable
 
 from tabulate import tabulate
 
@@ -33,6 +33,13 @@ if typing.TYPE_CHECKING:
     from .engine import Engine
     from .core import EngineMixin
 
+# Funtion type with any arguments and return a dict or None (device methods)
+MethodT = TypeVar(
+        "MethodT",
+        Callable[..., Union[dict, None]],
+        Callable[..., Awaitable[Union[dict, None]]]
+)
+
 logger = logging.getLogger(__name__)
 
 
@@ -215,7 +222,7 @@ class Device(object):
         else:
             raise DeviceError("Invalid attributes list, use class Attributes)")
 
-    def add_method(self, name: str, func: Callable[..., Any]):
+    def add_method(self, name: str, func: MethodT):
         self.methods.update({name: func})
 
     def del_method(self, name: str):