fix(bus): increase message bus buffer size from 16 to 64

Prevents potential backpressure under load when multiple channels
publish concurrently in gateway mode, where SDK callbacks blocking
on a full buffer can cause message loss or timeouts.

pkg/bus/bus.go

@@ -11,7 +11,7 @@ import (
 // ErrBusClosed is returned when publishing to a closed MessageBus.
 var ErrBusClosed = errors.New("message bus closed")
 
-const defaultBusBufferSize = 16
+const defaultBusBufferSize = 64
 
 type MessageBus struct {
 	inbound       chan InboundMessage