[fix] 修正SpanBuilder对象池借出Builder时，未设置Tracer的问题，该问题导致从池里借出来的Builder创建Sp…

…an时都没有Tracer，从而无法向上汇总统计

NewLife.Core/Log/ISpanBuilder.cs

@@ -112,17 +112,17 @@ public DefaultSpanBuilder() { }
     /// <param name="name"></param>
     public DefaultSpanBuilder(ITracer tracer, String name)
     {
-        Tracer = tracer;
-
-        Init(name);
+        Init(tracer, name);
     }
     #endregion
 
     #region 方法
     /// <summary>初始化。重用已有对象</summary>
+    /// <param name="tracer"></param>
     /// <param name="name"></param>
-    public void Init(String name)
+    public void Init(ITracer tracer, String name)
     {
+        Tracer = tracer;
         Name = name;
         MinCost = -1;
         StartTime = DateTime.UtcNow.ToLong();
@@ -241,7 +241,7 @@ internal void Return(IList<ISpan>? spans)
     public void Clear()
     {
         //!!! 不能清空Tracer，否则长时间Span完成时，Builder已被处理，Span无法创建新的Builder来统计埋点数据
-        Tracer = null;
+        //Tracer = null;
 
         Name = null!;
         StartTime = 0;

NewLife.Core/Log/ITracer.cs

@@ -209,7 +209,7 @@ protected virtual ISpanBuilder OnBuildSpan(String name)
     {
         var builder = BuilderPool.Get();
         if (builder is DefaultSpanBuilder dsb)
-            dsb.Init(name);
+            dsb.Init(this, name);
         else
             builder.Name = name;