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/update-collection/simple/rust.rs

@@ -1,6 +1,8 @@
 use qdrant_client::qdrant::{OptimizersConfigDiffBuilder, UpdateCollectionBuilder};
 
 pub async fn main() -> anyhow::Result<()> {
+    let client = qdrant_client::Qdrant::from_url("http://localhost:6334").build()?; // @hide
+
     client
         .update_collection(
             UpdateCollectionBuilder::new("{collection_name}").optimizers_config(