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/delete-vectors/simple/csharp.cs

@@ -1,9 +1,11 @@
-
+using Qdrant.Client; // @hide
+using Qdrant.Client.Grpc; // @hide
 
 public class Snippet
 {
 	public static async Task Run()
 	{
+		var client = new QdrantClient("localhost", 6334); // @hide
 		await client.DeleteVectorsAsync("{collection_name}", ["text", "image"], [0, 3, 10]);
 	}
 }

qdrant-landing/content/documentation/headless/snippets/delete-vectors/simple/go.go

@@ -7,6 +7,14 @@ import (
 )
 
 func Main() {
+	// @hide-start
+	client, err := qdrant.NewClient(&qdrant.Config{
+	    Host: "localhost",
+	    Port: 6334,
+	})
+	if err != nil { panic(err) }
+	// @hide-end
+
 	client.DeleteVectors(context.Background(), &qdrant.DeletePointVectors{
 		CollectionName: "{collection_name}",
 		PointsSelector: qdrant.NewPointsSelector(

qdrant-landing/content/documentation/headless/snippets/delete-vectors/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
                     .deleteVectorsAsync(
                         "{collection_name}", List.of("text", "image"), List.of(id(0), id(3), id(10)))

qdrant-landing/content/documentation/headless/snippets/delete-vectors/simple/rust.rs

@@ -3,6 +3,8 @@ use qdrant_client::qdrant::{
 };
 
 pub async fn main() -> anyhow::Result<()> {
+    let client = qdrant_client::Qdrant::from_url("http://localhost:6334").build()?; // @hide
+
     client
         .delete_vectors(
             DeletePointVectorsBuilder::new("{collection_name}")