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/peeringhandler.go

@@ -72,18 +72,25 @@ func NewPeeringHandler(db database.Store, logger *logger.Logger) *PeeringHandler
 	return h
 }
 
-// WantsMessage returns true if this handler wants to process messages of the given type
+// WantsMessage reports whether the handler should receive messages of the
+// given type. PeeringHandler only processes UPDATE messages, as these contain
+// the AS path information needed to extract peering relationships.
 func (h *PeeringHandler) WantsMessage(messageType string) bool {
 	// We only care about UPDATE messages that have AS paths
 	return messageType == "UPDATE"
 }
 
-// QueueCapacity returns the desired queue capacity for this handler
+// QueueCapacity returns the buffer size for the handler's message queue.
+// This value is used by the message dispatcher to allocate the channel
+// buffer when registering the handler.
 func (h *PeeringHandler) QueueCapacity() int {
 	return peeringHandlerQueueSize
 }
 
-// HandleMessage processes a message to extract AS paths
+// HandleMessage processes a BGP UPDATE message by storing its AS path
+// in memory for later batch processing. Messages with AS paths shorter
+// than minPathLengthForPeering are ignored as they cannot contain valid
+// peering information.
 func (h *PeeringHandler) HandleMessage(msg *ristypes.RISMessage) {
 	// Skip if no AS path or only one AS
 	if len(msg.Path) < minPathLengthForPeering {