refactor: move tool call parsing and formatting logic to a dedicated internal/toolcall package

internal/adapter/openai/chat_stream_runtime.go

@@ -1,6 +1,7 @@
 package openai
 
 import (
+	"ds2api/internal/toolcall"
 	"encoding/json"
 	"net/http"
 	"strings"
@@ -8,7 +9,6 @@ import (
 	openaifmt "ds2api/internal/format/openai"
 	"ds2api/internal/sse"
 	streamengine "ds2api/internal/stream"
-	"ds2api/internal/util"
 )
 
 type chatStreamRuntime struct {
@@ -102,7 +102,7 @@ func (s *chatStreamRuntime) sendDone() {
 func (s *chatStreamRuntime) finalize(finishReason string) {
 	finalThinking := s.thinking.String()
 	finalText := cleanVisibleOutput(s.text.String(), s.stripReferenceMarkers)
-	detected := util.ParseStandaloneToolCallsDetailed(finalText, s.toolNames)
+	detected := toolcall.ParseStandaloneToolCallsDetailed(finalText, s.toolNames)
 	if len(detected.Calls) > 0 && !s.toolCallsDoneEmitted {
 		finishReason = "tool_calls"
 		delta := map[string]any{