chore: unit test for cohere and handle stop curl

[vansangpfiev]

This pull request introduces several changes to the remote-engine component, focusing on enhancing the handling of streaming requests, improving status management, and adding new test cases. The most important changes include modifications to the StreamWriteCallback function, updates to the RemoteEngine::MakeStreamingChatCompletionRequest and RemoteEngine::HandleChatCompletion methods, and the addition of new test cases for the RemoteEngineTest suite.

Enhancements to streaming request handling:

• engine/extensions/remote-engine/remote_engine.cc: Added checks and updates to the StreamWriteCallback function to ensure the context->need_stop flag is correctly set and handled. [1] [2]

Improved status management:

• engine/extensions/remote-engine/remote_engine.cc: Added logic in RemoteEngine::MakeStreamingChatCompletionRequest to handle cases where no stop message is received, ensuring proper status reporting.
• engine/extensions/remote-engine/remote_engine.h: Introduced a new need_stop boolean member in the StreamContext struct to manage the stop condition for streaming requests.

Template rendering improvements:

• engine/extensions/remote-engine/remote_engine.cc: Updated RemoteEngine::HandleChatCompletion to ensure the model field is included in the response JSON if it is not already present.

New test cases:

• engine/test/components/test_remote_engine.cc: Added new test cases CohereRequest and CohereResponse to verify the correct handling of Cohere-specific requests and responses, including both streaming and non-streaming scenarios.## Describe Your Changes

Fixes Issues

• Closes #
• Closes #

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (for bug fixes / features)
• Created issues for follow-up changes or refactoring needed

[nguyenhoangthuan99]

LGTM