fix: return class in injectable decorator (#59)

* fix: return class in injectable decorator

# Proposal
Linked to #58

The issue with the Injectable decorator returning a string instead of the class itself likely stems from the decorator definition.

In the definition of Injectable, cls is treated as if it could potentially be a string (cls: str = None), which suggests that the decorator might be designed to accept optional parameters or configurations. However, if not handled properly, this design could lead to unexpected behavior, such as treating a class definition as a string.

# Correcting the Injectable Decorator
The decorator needs to correctly handle both cases: when it is used with and without parameters. Here’s a more standard way of creating a decorator that can optionally accept arguments

# Explanation
1. Decorator Factory: The Injectable function can now correctly handle being called either as @Injectable or @Injectable(). It uses a nested decorator function to apply the actual class modifications.

2. Class Modifications: It checks if the class has an __init__ method defined and, if not, assigns a default one. It then parses dependencies, sets necessary attributes, and applies injection.

3. Handling Arguments: The outer function (Injectable) checks if it is given a class directly (cls is not None). If so, it directly returns the decorator applied to the class. Otherwise, it returns the decorator function itself, allowing for further customization or arguments.

* fix: use elipsis instead of pass

nest/core/decorators/injectable.py

@@ -1,25 +1,27 @@
 from injector import inject
 
 from nest.common.constants import DEPENDENCIES, INJECTABLE_NAME, INJECTABLE_TOKEN
-from nest.core.decorators.utils import get_instance_variables, parse_dependencies
-
-
-def Injectable(cls: str = None):
-    def __init__(self, *args, **kwargs):
-        ...
-
-    if "__init__" in cls.__dict__:
-        pass
-    else:
-        cls.__init__ = __init__
-
-    dependencies = parse_dependencies(cls)
-
-    setattr(cls, DEPENDENCIES, dependencies)
-
-    setattr(cls, INJECTABLE_TOKEN, True)
-    setattr(cls, INJECTABLE_NAME, cls.__name__)
-
-    inject(cls)
-
-    return cls
+from nest.core.decorators.utils import parse_dependencies
+
+
+def Injectable(cls=None, *args, **kwargs):
+    def decorator(inner_cls):
+        if "__init__" not in inner_cls.__dict__:
+            def __init__(self, *args, **kwargs):
+                ...
+            inner_cls.__init__ = __init__
+
+        dependencies = parse_dependencies(inner_cls)
+
+        setattr(inner_cls, DEPENDENCIES, dependencies)
+        setattr(inner_cls, INJECTABLE_TOKEN, True)
+        setattr(inner_cls, INJECTABLE_NAME, inner_cls.__name__)
+
+        inject(inner_cls)
+
+        return inner_cls
+
+    if cls is not None:
+        return decorator(cls)
+
+    return decorator