feat: implement coinank openapi netPositions interface (#1258)

- implement Net long & Net short interface

provider/coinank/net_positions_test.go

@@ -0,0 +1,25 @@
+package coinank
+
+import (
+	"context"
+	"encoding/json"
+	"nofx/provider/coinank/coinank_enum"
+	"testing"
+	"time"
+)
+
+func TestNetPositions(t *testing.T) {
+	client := NewCoinankClient(coinank_enum.MainUrl, TestApikey)
+	resp, err := client.NetPositions(context.TODO(), coinank_enum.Binance, "BTCUSDT", coinank_enum.Hour1, time.Now().UnixMilli(), 10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resp[0].Begin <= 0 {
+		t.Errorf("begin timestamp error")
+	}
+	res, err := json.Marshal(resp)
+	if err != nil {
+		t.Error(err)
+	}
+	t.Logf("%s", res)
+}