fix: Updated ThreadMessage struct with latest fields based on OpenAI docs (#792)

* fix: Updated ThreadMessage struct with latest fields based on OpenAI docs

* fix: Reverted FileIDs for backward compatibility of v1

thread.go

@@ -83,6 +83,7 @@ type ModifyThreadRequest struct {
 type ThreadMessageRole string
 
 const (
+	ThreadMessageRoleAssistant ThreadMessageRole = "assistant"
 	ThreadMessageRoleUser      ThreadMessageRole = "user"
 )
 
@@ -90,9 +91,19 @@ type ThreadMessage struct {
 	Role        ThreadMessageRole  `json:"role"`
 	Content     string             `json:"content"`
 	FileIDs     []string           `json:"file_ids,omitempty"`
+	Attachments []ThreadAttachment `json:"attachments,omitempty"`
 	Metadata    map[string]any     `json:"metadata,omitempty"`
 }
 
+type ThreadAttachment struct {
+	FileID string                 `json:"file_id"`
+	Tools  []ThreadAttachmentTool `json:"tools"`
+}
+
+type ThreadAttachmentTool struct {
+	Type string `json:"type"`
+}
+
 type ThreadDeleteResponse struct {
 	ID      string `json:"id"`
 	Object  string `json:"object"`