Fix: Proper Blockwise Handling for Initial GET and DELETE Requests

Corrected the handling of initial requests for GET and DELETE operations in
the CoAP blockwise implementation. Previously, the code allowed the use of
message types Acknowledge (ACK) or Reset (RST) for the initial request.

net/blockwise/blockwise.go

@@ -386,6 +386,10 @@ func (b *BlockWise[C]) handleReceivedMessage(w *responsewriter.ResponseWriter[C]
 		next(w, r)
 		return nil
 	case codes.GET, codes.DELETE:
+		// For GET and DELETE requests in CoAP, the initial request cannot have the message type of Acknowledge (ACK) or Reset (RST)
+		if r.Type() == message.Acknowledgement || r.Type() == message.Reset {
+			return fmt.Errorf("invalid message type(%v) for code(%v)", r.Type(), r.Code())
+		}
 		maxSZX = fitSZX(r, message.Block2, maxSZX)
 		block, errG := r.GetOptionUint32(message.Block2)
 		if errG == nil {