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

edits.go

@@ -32,7 +32,7 @@ type EditsResponse struct {
 
 // Perform an API call to the Edits endpoint.
 func (c *Client) Edits(ctx context.Context, request EditsRequest) (response EditsResponse, err error) {
-	req, err := c.requestBuilder.build(ctx, http.MethodPost, c.fullURL("/edits", fmt.Sprint(request.Model)), request)
+	req, err := c.requestBuilder.Build(ctx, http.MethodPost, c.fullURL("/edits", fmt.Sprint(request.Model)), request)
 	if err != nil {
 		return
 	}