Job methods docstrings (#1772)

* Improve docstrings on `connections`

* Enhanced Job methods docstrings & Serialization Protocol

This adds docstrings to all Job methods in a standard format.
It also implements a `serializer` protocol.

* Excludes `Protocol` (keeping compatibility with < 3.8)

* Add docstrings & type annotation to the `job` decorator

* Docstrings for the `defaults` vars

* Add deprecation warning to Connection context manager

* Fix Types

1 files changed, 9 insertions, 2 deletions

diff --git a/rq/serializers.py b/rq/serializers.py
index 00fd0a7..9e63bc7 100644
--- a/rq/serializers.py
+++ b/rq/serializers.py
@@ -1,6 +1,7 @@
 from functools import partial
 import pickle
 import json
+from typing import Optional, Union
 
 from .utils import import_attribute
 
@@ -20,11 +21,17 @@ class JSONSerializer():
         return json.loads(s.decode('utf-8'), *args, **kwargs)
 
 
-def resolve_serializer(serializer: str):
+def resolve_serializer(serializer=None):
     """This function checks the user defined serializer for ('dumps', 'loads') methods
     It returns a default pickle serializer if not found else it returns a MySerializer
     The returned serializer objects implement ('dumps', 'loads') methods
-    Also accepts a string path to serializer that will be loaded as the serializer
+    Also accepts a string path to serializer that will be loaded as the serializer.
+
+    Args:
+        serializer (Callable): The serializer to resolve.
+    
+    Returns:
+        serializer (Callable): An object that implements the SerializerProtocol
     """
     if not serializer:
         return DefaultSerializer