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

moderation.go

@@ -63,7 +63,7 @@ type ModerationResponse struct {
 // Moderations — perform a moderation api call over a string.
 // Input can be an array or slice but a string will reduce the complexity.
 func (c *Client) Moderations(ctx context.Context, request ModerationRequest) (response ModerationResponse, err error) {
-	req, err := c.requestBuilder.build(ctx, http.MethodPost, c.fullURL("/moderations", request.Model), request)
+	req, err := c.requestBuilder.Build(ctx, http.MethodPost, c.fullURL("/moderations", request.Model), request)
 	if err != nil {
 		return
 	}