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/streamer/streamer.go

@@ -19,6 +19,7 @@ import (
 	"git.eeqj.de/sneak/routewatch/internal/ristypes"
 )
 
+// Configuration constants for the RIS Live streamer.
 const (
 	risLiveURL = "https://ris-live.ripe.net/v1/stream/?format=json&" +
 		"client=https%3A%2F%2Fgit.eeqj.de%2Fsneak%2Froutewatch"
@@ -36,16 +37,22 @@ const (
 	backpressureSlope     = 2.0 // Slope for linear drop probability increase
 )
 
-// MessageHandler is an interface for handling RIS messages
+// MessageHandler defines the interface for processing RIS messages.
+// Implementations must specify which message types they want to receive,
+// how to process messages, and their desired queue capacity.
 type MessageHandler interface {
-	// WantsMessage returns true if this handler wants to process messages of the given type
+	// WantsMessage returns true if this handler wants to process messages of the given type.
 	WantsMessage(messageType string) bool
 
-	// HandleMessage processes a RIS message
+	// HandleMessage processes a RIS message. This method is called from a dedicated
+	// goroutine for each handler, so implementations do not need to be goroutine-safe
+	// with respect to other handlers.
 	HandleMessage(msg *ristypes.RISMessage)
 
-	// QueueCapacity returns the desired queue capacity for this handler
-	// Handlers that process quickly can have larger queues
+	// QueueCapacity returns the desired queue capacity for this handler.
+	// Handlers that process quickly can have larger queues to buffer bursts.
+	// When the queue fills up, messages will be dropped according to the
+	// backpressure algorithm.
 	QueueCapacity() int
 }