test : add comprehensive unit tests for deepseek-llm plugin

[goblin0xcrypto]

Add Comprehensive Test Coverage for DeepSeekLLM Plugin

Summary

This PR adds comprehensive unit tests for the DeepSeekLLM plugin to improve code quality and maintainability.

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Test Coverage

⚙️ Configuration & Initialization Tests

• Test successful initialization with provided configuration
• Test fallback to default model (deepseek-chat) when model is not specified
• Test validation that raises ValueError when API key is missing
• Test configuration with custom base URL and model

🧠 Core Functionality Tests

• Test successful API request without tool calls (returns None)
• Test successful API request with single tool call
• Test successful API request with multiple tool calls
• Test handling of empty response choices (returns None)
• Test handling of invalid JSON responses (returns empty CortexOutputModel)

🛠️ Error Handling Tests

• Test graceful error handling for API exceptions (returns None)
• Test malformed message handling (missing role or content)

📜 Message History Tests

• Test API call with message history
• Test correct message formatting and ordering

📊 Performance & Monitoring Tests

• Test I/O provider timing metrics collection (llm_start_time and llm_end_time)
• Test timeout configuration is properly passed to API

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Files Changed

• tests/llm/plugins/test_deepseek_llm.py (new)