Release Python SDK 0.7.1

[JJasonSun]

Summary

• Bump the Python package, generated-client metadata, and OpenAPI contract to 0.7.1.
• Publish the completed open-source and security work under a dated 0.7.1 changelog section.
• Refresh the locked project version.

Checklist

• I kept this change within the supported server SDK scope.
• I did not add browser/client-side patterns that expose CALL-E API keys.
• I did not include private collaboration links or unconfirmed public repository references.
• I updated tests, examples, or docs when behavior changed.
• I updated the changelog when the change affects package users.
• I ran the relevant local checks.

Local checks

bash scripts/validate.sh

Passed: 51 tests, Ruff, mypy, OpenAPI and public-repository checks, 0.7.1 wheel and sdist builds, Twine validation, artifact verification, and fresh install smoke tests.

Merging this PR does not publish PyPI.