cmd/geth, consensus/ethash: add support for --miner.notify.full flag (#22558)

The PR implements the --miner.notify.full flag that enables full pending block
notifications. When this flag is used, the block notifications sent to mining
endpoints contain the complete block header JSON instead of a work package
array.

Co-authored-by: AlexSSD7 <alexandersadovskyi7@protonmail.com>
Co-authored-by: Martin Holst Swende <martin@swende.se>

consensus/ethash/sealer.go

@@ -358,7 +358,16 @@ func (s *remoteSealer) makeWork(block *types.Block) {
 // new work to be processed.
 func (s *remoteSealer) notifyWork() {
 	work := s.currentWork
-	blob, _ := json.Marshal(work)
+
+	// Encode the JSON payload of the notification. When NotifyFull is set,
+	// this is the complete block header, otherwise it is a JSON array.
+	var blob []byte
+	if s.ethash.config.NotifyFull {
+		blob, _ = json.Marshal(s.currentBlock.Header())
+	} else {
+		blob, _ = json.Marshal(work)
+	}
+
 	s.reqWG.Add(len(s.notifyURLs))
 	for _, url := range s.notifyURLs {
 		go s.sendNotification(s.notifyCtx, url, blob, work)