func NewSpanContext(
	traceID uint64,
	spanID uint64,
	baggage map[string]string,
) SpanContext {
	return spanContext{
		traceID: traceID,
		spanID:  spanID,
		baggage: baggage,
	}
}
NewSpanContext creates a new SpanContext
package core
import (
	"fmt"
	"sync"
	"time"
	opentracing "github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/log"
)
type SpanContext interface {
	opentracing.SpanContext
	TraceID() string
	SpanID() string
	BaggageItem(key string) string
}
type spanContext struct {
	traceID uint64
	spanID uint64
	baggage map[string]string  
}