Fix type-checking errors in snippets (code only, no .md)

This commit both:
- Fixes pre-existing mistakes in snippets, aka wrong code samples.
- Adds hidden (`@hide`) statements that do not appear in the docs,
  but satisfy typecheckers.

qdrant-landing/content/documentation/headless/snippets/retrieve-points/simple/java.java

@@ -6,6 +6,11 @@ import java.util.List;
 
 public class Snippet {
         public static void run() throws Exception {
+                // @hide-start
+                io.qdrant.client.QdrantClient client =
+                    new io.qdrant.client.QdrantClient(io.qdrant.client.QdrantGrpcClient.newBuilder("localhost", 6334, false).build());
+                // @hide-end
+
                 client
                     .retrieveAsync("{collection_name}", List.of(id(0), id(30), id(100)), false, false, null)
                     .get();