Refactor AgentMarket class to use abstract methods

[coderabbitai]

Refactor the AgentMarket class to make it an abstract class and use the @abstractmethod decorator for methods currently raising NotImplementedError. This change will enforce the implementation of necessary methods in subclasses, providing compile-time warnings if they are not implemented. This approach will enhance code robustness and prevent runtime errors. See the discussion for more details: #352 (comment)