Add comprehensive godoc documentation to handler.go

Expand documentation comments for SimpleHandler type and its methods
to better explain their purpose, parameters, and behavior.

internal/routewatch/ashandler.go

@@ -171,7 +171,11 @@ func (h *ASHandler) flushBatchLocked() {
 	h.lastFlush = time.Now()
 }
 
-// Stop gracefully stops the handler and flushes remaining batches
+// Stop gracefully shuts down the ASHandler by signaling the background flush
+// goroutine to terminate and waiting for it to complete. Any pending ASN
+// operations in the current batch are flushed to the database before Stop
+// returns. This method should be called during application shutdown to ensure
+// no data is lost.
 func (h *ASHandler) Stop() {
 	close(h.stopCh)
 	h.wg.Wait()