Fix ProviderConfig to include rate_limit field

- Add rate_limit field to ProviderConfig model with default value 0.0
- This fixes AttributeError when BaseProviderHandler tries to access rate_limit
- The providers.json file already contains rate_limit for all providers

aisbf/config.py

@@ -34,6 +34,7 @@ class ProviderConfig(BaseModel):
     endpoint: str
     type: str
     api_key_required: bool
+    rate_limit: float = 0.0
 
 class RotationConfig(BaseModel):
     providers: List[Dict]