feat(ChatDeepSeek): Add deepseek support

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Pull Request Overview

This PR adds support for the DeepSeek AI platform by implementing a new ChatDeepSeek provider class that integrates with the existing chatlas framework.

• Implements ChatDeepSeek class as a wrapper around the OpenAI provider with DeepSeek-specific configurations
• Adds comprehensive test coverage for the new provider including streaming, tools, and turns interface
• Updates documentation to include DeepSeek in the supported models list

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
chatlas/_provider_deepseek.py	Implements the main ChatDeepSeek provider class with DeepSeek API integration
tests/test_provider_deepseek.py	Adds comprehensive test suite for DeepSeek provider functionality
chatlas/init.py	Exports the new ChatDeepSeek class in the main module
docs/get-started/models.qmd	Adds DeepSeek to the supported models documentation table
docs/_quarto.yml	Includes ChatDeepSeek in the documentation generation config
CHANGELOG.md	Documents the new DeepSeek feature addition

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