Handle non-JSON Cloud Query error responses

[adamtheturtle]

Summary

• raise a response-carrying CloudRecoError for documented empty or non-JSON Cloud Query 4xx responses
• cover both sync and async clients using the new forced-failure support in vws-python-mock==2026.8.4.1
• remove the obsolete direct PyTorch development dependencies now that the mock uses OpenCV

The mock support was merged in vws-python-mock#3315 and released by workflow run 30913240037.

Validation

• pytest: 325 passed with 100% coverage
• all pre-commit and manual hooks
• all pre-push hooks, including mypy, pyright, pyrefly, ty, and package checks

Closes #3093

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Note

Low Risk
Localized error-handling change in Cloud Query with matching tests; dependency cleanup only affects dev/test installs.

Overview
Cloud Query sync and async clients now treat documented 4xx responses with empty or non-JSON bodies as CloudRecoError (with the HTTP response attached) instead of surfacing JSONDecodeError. Parsing is centralized in a single response_body load; successful responses with invalid JSON still raise JSONDecodeError.

Dev tooling drops explicit PyTorch/torchvision pins and the CPU PyTorch uv index, and bumps vws-python-mock to 2026.8.4.1 so tests can force Cloud Query failures via CloudQueryFailureResponse. New tests cover empty and arbitrary-text 4xx bodies plus malformed 200 responses for both clients.

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