Function encode_upsert_request 

pub fn encode_upsert_request(points: &[Point]) -> Vec<u8> 

Encode an upsert (insert/update) request to JSON.

Generates JSON for PUT /collections/{collection}/points

Example output:

{
  "points": [
    { "id": "abc123", "vector": [0.1, 0.2], "payload": {"name": "test"} }
  ]
}