docs: clarify that if let Ok guard on from_value is infallible for serde_json::Value

Add inline comment explaining that deserializing into serde_json::Value always
succeeds, so the Ok branch always fires. The guard future-proofs against typed
additionalProperties schemas where the conversion could fail.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: charlie-zhang109

.generator/src/generator/templates/model_simple.j2

@@ -119,6 +119,7 @@ impl<'de> Deserialize<'de> for {{ name }} {
 
                 while let Some((k, v)) = map.next_entry::<String, serde_json::Value>()? {
                     {%- if additionalProperties != false and model.get("x-keep-typed-in-additional-properties") %}
+                    // from_value::<serde_json::Value> is infallible; the Ok guard future-proofs typed AP schemas.
                     if let Ok(ap_value) = serde_json::from_value(v.clone()) {
                         additional_properties.insert(k.clone(), ap_value);
                     }