feat: add proactive push notification processing to WithReader

- Add push notification processing to Conn.WithReader method
- Process notifications immediately before every read operation
- Provides proactive notification handling vs reactive processing
- Add proper error handling with internal.Logger
- Non-blocking implementation that doesn't break Redis operations
- Complements existing processing in Pool.Put and isHealthyConn

Benefits:
- Immediate processing when notifications arrive
- Called before every read operation for optimal timing
- Prevents notification backlog accumulation
- More responsive to Redis cluster changes
- Better user experience during migrations
- Optimal placement for catching asynchronous notifications

Implementation:
- Type-safe interface assertion for processor
- Context-aware error handling with logging
- Maintains backward compatibility
- Consistent with existing pool patterns
- Three-layer processing strategy: WithReader (proactive) + Pool.Put + isHealthyConn (reactive)

Use cases:
- MOVING/MIGRATING/MIGRATED notifications for slot migrations
- FAILING_OVER/FAILED_OVER notifications for failover scenarios
- Real-time cluster topology change awareness
- Improved connection utilization efficiency

internal/pool/conn.go

@@ -7,6 +7,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/redis/go-redis/v9/internal"
 	"github.com/redis/go-redis/v9/internal/proto"
 	"github.com/redis/go-redis/v9/internal/pushnotif"
 )
@@ -77,11 +78,23 @@ func (cn *Conn) RemoteAddr() net.Addr {
 func (cn *Conn) WithReader(
 	ctx context.Context, timeout time.Duration, fn func(rd *proto.Reader) error,
 ) error {
+	// Process any pending push notifications before executing the read function
+	// This ensures push notifications are handled as soon as they arrive
+	if cn.PushNotificationProcessor != nil {
+		// Type assert to the processor interface
+		if err := cn.PushNotificationProcessor.ProcessPendingNotifications(ctx, cn.rd); err != nil {
+			// Log the error but don't fail the read operation
+			// Push notification processing errors shouldn't break normal Redis operations
+			internal.Logger.Printf(ctx, "push: error processing pending notifications in WithReader: %v", err)
+		}
+	}
+
 	if timeout >= 0 {
 		if err := cn.netConn.SetReadDeadline(cn.deadline(ctx, timeout)); err != nil {
 			return err
 		}
 	}
+
 	return fn(cn.rd)
 }