test: create tests for belief extractor agent

Includes changes in schemas. Change type of `norms` in `Program` imperceptibly, big changes in schema of `BeliefMessage` to support deleting beliefs.

ref: N25B-380

src/control_backend/schemas/belief_message.py

@@ -6,18 +6,27 @@ class Belief(BaseModel):
     Represents a single belief in the BDI system.
 
     :ivar name: The functor or name of the belief (e.g., 'user_said').
-    :ivar arguments: A list of string arguments for the belief.
-    :ivar replace: If True, existing beliefs with this name should be replaced by this one.
+    :ivar arguments: A list of string arguments for the belief, or None if the belief has no
+        arguments.
     """
 
     name: str
-    arguments: list[str]
-    replace: bool = False
+    arguments: list[str] | None
 
 
 class BeliefMessage(BaseModel):
     """
-    A container for transporting a list of beliefs between agents.
+    A container for communicating beliefs between agents.
+
+    :ivar create: Beliefs to create.
+    :ivar delete: Beliefs to delete.
+    :ivar replace: Beliefs to replace. Deletes all beliefs with the same name, replacing them with
+        one new belief.
     """
 
-    beliefs: list[Belief]
+    create: list[Belief] = []
+    delete: list[Belief] = []
+    replace: list[Belief] = []
+
+    def has_values(self) -> bool:
+        return len(self.create) > 0 or len(self.delete) > 0 or len(self.replace) > 0