Add OpenSearch and SearchPage functionality for DuckDuckGo

Introduced the `OpenSearch` method and `SearchPage` interface to streamline search operations and allow for loading more results dynamically. Updated dependencies and modified the DuckDuckGo CLI to utilize these enhancements.

sites/duckduckgo/duckduckgo.go

@@ -77,6 +77,21 @@ func deferClose(cl io.Closer) {
 	}
 }
 
+func (c Config) OpenSearch(ctx context.Context, b extractor.Browser, query string) (SearchPage, error) {
+	u := c.ToSearchURL(query)
+
+	slog.Info("searching", "url", u, "query", query, "config", c, "browser", b)
+	doc, err := b.Open(ctx, u.String(), extractor.OpenPageOptions{})
+	if err != nil {
+		if doc != nil {
+			_ = doc.Close()
+		}
+		return nil, fmt.Errorf("failed to open url: %w", err)
+	}
+
+	return searchPage{doc}, nil
+}
+
 func (c Config) Search(ctx context.Context, b extractor.Browser, query string) ([]Result, error) {
 	u := c.ToSearchURL(query)