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/overwrite-payload/by-point-id/rust.rs

@@ -3,6 +3,8 @@ use qdrant_client::Payload;
 use serde_json::json;
 
 pub async fn main() -> anyhow::Result<()> {
+    let client = qdrant_client::Qdrant::from_url("http://localhost:6334").build()?; // @hide
+
     client
         .overwrite_payload(
             SetPayloadPointsBuilder::new(