fix: update FastAPI to >=0.120.2 to address CVE-2025-62727

[Cole Murray (ColeMurray)]

Updates FastAPI minimum version from 0.90.1 to 0.120.2 across all dependency groups to address Starlette vulnerability CVE-2025-62727.

This updates:

• Main optional dependency
• Dev dependencies
• Examples dependencies
• poetry.lock file

Reference: https://www.cve.org/CVERecord?id=CVE-2025-62727

[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 Cole Murray (@ColeMurray) 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.

[Cole Murray (ColeMurray)]

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 Cole Murray (@ColeMurray) 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.

updated