Batch dependency updates (#327)

Consolidates 5 Dependabot PRs into one (all lockfile-only, core dep
constraints are already wide enough):

- cloudpickle 3.1.1 → 3.1.2
- fastapi 0.128.0 → 0.128.5
- mypy 1.18.2 → 1.19.1
- protobuf 6.33.0 → 6.33.5
- rich 14.2.0 → 14.3.2

Supersedes #321, #323, #324, #325, #326

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: chrisguidry