Refactor Anthropic import to langchain_anthropic and update model to v3

[donbr]

• Transition Anthropic API import to the langchain_anthropic package for enhanced compatibility.
• Upgrade the AI model to claude-3-sonnet-20240229 for improved performance and features.

[cla-bot]

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[donbr]

The contributor license agreement has been signed.

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the username @donbr on file. In order for us to review and merge your code, please complete the Individual Contributor License Agreement here https://forms.gle/AQFbtkWRoHXUgipM6 .

This process is done manually on our side, so after signing the form one of the maintainers will add you to the contributors list.

For more details about why we have a CLA and other contribution guidelines please see: https://github.com/langchain-ai/langserve/blob/main/CONTRIBUTING.md.

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the username @donbr on file. In order for us to review and merge your code, please complete the Individual Contributor License Agreement here https://forms.gle/AQFbtkWRoHXUgipM6 .

This process is done manually on our side, so after signing the form one of the maintainers will add you to the contributors list.

For more details about why we have a CLA and other contribution guidelines please see: https://github.com/langchain-ai/langserve/blob/main/CONTRIBUTING.md.