🔨 refactor(base.py): make function_name and initialize methods abstract

This commit makes the `function_name` and `initialize` methods abstract in the `CustomChain` and `CustomAgentExecutor` classes. This is done to enforce the implementation of these methods in the subclasses of these classes. This change improves the code quality and readability by making the code more explicit and easier to understand.

src/backend/langflow/interface/base.py

@@ -91,10 +91,12 @@ class CustomChain(Chain, ABC):
     """Custom chain"""
 
     @staticmethod
+    @abstractmethod
     def function_name():
         return "CustomChain"
 
     @classmethod
+    @abstractmethod
     def initialize(cls, *args, **kwargs):
         pass
 
@@ -109,10 +111,12 @@ class CustomAgentExecutor(AgentExecutor, ABC):
     """Custom chain"""
 
     @staticmethod
+    @abstractmethod
     def function_name():
         return "CustomChain"
 
     @classmethod
+    @abstractmethod
     def initialize(cls, *args, **kwargs):
         pass