move request_builder into internal pkg (#304) (#329)

* move request_builder into internal pkg (#304)

* add some test for internal.RequestBuilder

* add a test for openai.GetEngine

image.go

@@ -44,7 +44,7 @@ type ImageResponseDataInner struct {
 // CreateImage - API call to create an image. This is the main endpoint of the DALL-E API.
 func (c *Client) CreateImage(ctx context.Context, request ImageRequest) (response ImageResponse, err error) {
 	urlSuffix := "/images/generations"
-	req, err := c.requestBuilder.build(ctx, http.MethodPost, c.fullURL(urlSuffix), request)
+	req, err := c.requestBuilder.Build(ctx, http.MethodPost, c.fullURL(urlSuffix), request)
 	if err != nil {
 		return
 	}