deps(python): bump multidict from 6.7.0 to 6.7.1 in /backend

[dependabot]

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Summary by cubic

Upgrade multidict from 6.7.0 to 6.7.1 in the backend to pull in upstream bug fixes and updated wheels. Patch release; no breaking changes expected.

^{Written for commit afc2ed7. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 2 files

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dependabot]

Dependabot attempted to update this pull request, but because the branch dependabot/uv/backend/multidict-6.7.1 is protected it was unable to do so.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.