fix: restore on_retry param names with proper override hook comment

Author: fgogolli

src/orb/infrastructure/resilience/strategy/exponential.py

@@ -92,12 +92,16 @@ def get_delay(self, attempt: int) -> float:
 
         return delay
 
-    def on_retry(self, _attempt: int, _exception: Exception) -> None:
+    def on_retry(self, attempt: int, exception: Exception) -> None:
         """
         Handle retry event (logging, metrics).
 
+        This is a hook for subclasses to override — e.g. AWSRetryStrategy
+        logs the attempt number and exception details here.
+
         Args:
             attempt: Current attempt number (0-based)
             exception: Exception that occurred
         """
-        # This method can be extended for metrics collection in the future
+        # Base implementation is intentionally empty — subclasses override this
+        # to add logging, metrics, or other side effects on each retry.