Add unit tests for OpenAI plugin and establish coding standards

- Introduced comprehensive unit tests for the OpenAI plugin, covering SSE parsing, sentinel matching, delta extraction, request building, and more.
- Created a new markdown file detailing coding and naming conventions for the dstalk project, including guidelines for comments, naming rules, code organization, and memory management practices.

docs/reference/plugin-abi.md

@@ -110,7 +110,7 @@ Linux/macOS 通常共享 libc，但静态链接或不同 libc 版本时同样可
 ### 4.2 重复注册
 
 同一 `name` 不可重复注册：第二次调用返回 `-2`（`service_registry.cpp:13`）。插件应检查返回
-值，在共享服务名（如 `"ai.deepseek"`）的场景中避免冲突。
+值，在共享服务名（如 `"ai.openai"`）的场景中避免冲突。
 
 ### 4.3 版本协商