Fix the following issue:
I want the github.com/8treenet/freedom/infra/kafka package to provide a stateful Kafka producer API for Freedom applications. The entry point should be kafka.GetProducer() kafka.Producer, where Producer exposes Start(addrs []string, config *sarama.Config), NewMsg(topic string, content []byte) *kafka.Msg, and Restart() error; the concrete *kafka.ProducerImpl should also support Close() error for lifecycle cleanup.
Calling Start([]string{"127.0.0.1:9092"}, cfg) should remember the broker addresses and Sarama config for the producer lifecycle, and it should force cfg.Producer.Return.Errors and cfg.Producer.Return.Successes to true so synchronous sends can report their result. After the Freedom application boots with configured broker addresses, publishing kafka.GetProducer().NewMsg("orders", []byte("paid")).SetMessageKey("order-1").SetHeader(map[string]interface{}{"x-request-id":"r1", "attempt": 2}).Publish() should send one Sarama producer message to topic orders, with value paid, key order-1, and headers x-request-id: r1 and attempt: 2. If no message key is set, Publish should generate a non-empty uppercase UUID-style key with dashes removed before sending.
Msg.SetHeader should be chainable and should merge additional header maps into any existing headers. Msg.GetHeader, Msg.SetMessageKey, and Msg.GetMessageKey should expose the current message headers and key consistently before publish. If Publish is called before the producer has an initialized Sarama sync producer, it should return an error equivalent to producer is not initialized instead of panicking.
I also need producer middleware support through kafka.InstallMiddleware(...kafka.ProducerHandler), where ProducerHandler is func(*kafka.Msg). Installed handlers should run in order when Msg.Publish calls Msg.Next; a handler can call Next to continue, call Stop to prevent the send, and inspect IsStopped or GetExecution for message state. Restart() should close the current producer connection and then dial again using the stored addresses and config, and Close() should be a no-op when no producer connection is active.