Fix ID formatting in Problem class: Change separator from underscore to hyphen in the generated ID

convert.py

@@ -12,7 +12,7 @@ class Problem(BaseModel):
     
     def to_dict(self):
         return {
-            "id": f"{self.year}_imo_{self.problem_id}",
+            "id": f"{self.year}-imo-{self.problem_id}",
             "problem": self.problem,
             "solution": self.solution
         }