Improve typing for messages module (#634)

Author: tyzhnenko

blacksheep/contents.py

@@ -14,7 +14,7 @@ def __init__(self, content_type: bytes, data: bytes):
         self.body = data
         self.length = len(data)
 
-    async def read(self):
+    async def read(self) -> bytes:
         return self.body
 
 

blacksheep/headers.py

@@ -20,7 +20,7 @@ def __eq__(self, other):
 
 
 class Headers:
-    def __init__(self, values: list[tuple[bytes, bytes]] = None):
+    def __init__(self, values: list[tuple[bytes, bytes]] | None = None):
         if values is None:
             values = []
         self.values = values