docs: add Qwen integration guide and update qwq documentation

[TBice123123]

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Description:
Add documentation for Qwen integration in LangChain, including setup instructions, usage examples, and configuration details. Update related qwq documentation to reflect current best practices and improve clarity for users.

This PR enhances the documentation ecosystem by:

• Adding a new guide for integrating Qwen models
• Updating outdated or incomplete qwq documentation
• Improving structure and readability of relevant sections

Issue: N/A
Dependencies: None

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Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ready	Preview	Comment	Sep 4, 2025 2:33pm

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32817 will not alter performance

_{Comparing TBice123123:docs/qwen (ad424ee) with master (aa63de9)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32817 will not alter performance

_{Comparing TBice123123:docs/qwen (ad424ee) with master (aa63de9)}

Summary

✅ 14 untouched benchmarks