refactor: remove Tracer from middleware implementations and related debugging functionality

internal/net/gphttp/middleware/modify_response.go

@@ -6,19 +6,16 @@ import (
 
 type modifyResponse struct {
 	ModifyRequestOpts
-	Tracer
 }
 
 var ModifyResponse = NewMiddleware[modifyResponse]()
 
 // modifyResponse implements ResponseModifier.
 func (mr *modifyResponse) modifyResponse(resp *http.Response) error {
-	mr.AddTraceResponse("before modify response", resp)
 	if !mr.needVarSubstitution {
 		mr.modifyHeaders(resp.Request, resp.Header)
 	} else {
 		mr.modifyHeadersWithVarSubstitution(resp.Request, resp, resp.Header)
 	}
-	mr.AddTraceResponse("after modify response", resp)
 	return nil
 }