fix(database/gredis): gredis support get raw client (#4306)

Fixes https://github.com/gogf/gf/issues/4298
Fixes https://github.com/gogf/gf/issues/2196
Fixes https://github.com/gogf/gf/issues/2135
```go
import goredis "github.com/redis/go-redis/v9"

func ExampleUsage(ctx context.Context, redis *Redis) error {
	client := redis.Client()
	universalClient, ok := client.(goredis.UniversalClient)
	if !ok {
		return errors.New("failed to assert to UniversalClient")
	}

	// Use universalClient for advanced operations like Pipeline
	pipe := universalClient.Pipeline()
	pipe.Set(ctx, "key1", "value1", 0)
	pipe.Set(ctx, "key2", "value2", 0)
	results, err := pipe.Exec(ctx)
	if err != nil {
		return err
	}
	// ... handle results
	return nil
}
```

---------

Co-authored-by: hailaz <739476267@qq.com>

database/gredis/gredis_adapter.go

@@ -30,6 +30,10 @@ type AdapterGroup interface {
 	GroupString() IGroupString
 }
 
+// RedisRawClient is a type alias for any, representing the raw underlying redis client.
+// Implementations should return their concrete client type as this interface.
+type RedisRawClient any
+
 // AdapterOperation is the core operation functions for redis.
 // These functions can be easily overwritten by custom implements.
 type AdapterOperation interface {
@@ -43,6 +47,11 @@ type AdapterOperation interface {
 
 	// Close closes current redis client, closes its connection pool and releases all its related resources.
 	Close(ctx context.Context) (err error)
+
+	// Client returns the underlying redis client instance.
+	// This method provides access to the raw redis client for advanced operations
+	// that are not covered by the standard redis adapter interface.
+	Client() RedisRawClient
 }
 
 // Conn is an interface of a connection from universal redis client.