Merge upstream PR sigoden#1511: serialize the stream flag

Integrate the exact upstream PR head so OpenAI-compatible requests always
carry the configured stream boolean. The combined streaming follow-up keeps
this source hunk and adds focused true/false coverage.

Source: sigoden#1511
Head: 63ecb71

Author: ei-grad

src/client/openai.rs

@@ -328,9 +328,7 @@ pub fn openai_build_chat_completions_body(data: ChatCompletionsData, model: &Mod
     if let Some(v) = top_p {
         body["top_p"] = v.into();
     }
-    if stream {
-        body["stream"] = true.into();
-    }
+    body["stream"] = stream.into();
     if let Some(functions) = functions {
         body["tools"] = functions
             .iter()