feat(examples): backport download_benchmark_assets to 25.9

[marcvivesmassana]

Summary

• Backports the download_benchmark_assets helper from https://github.com/flexcompute/compute/pull/6942 into the release-candidate/25.9 client line.
• Adds flow360/examples/benchmark_assets.py (pure urllib + json, no new dependencies) and exports download_benchmark_assets from flow360.examples.
• Lets the Flow360 benchmark reproducer notebooks fetch a case's public root asset and reference data with no credentials or private project id, on the 25.9 client family the cases are validated against.

Context

The helper currently ships only on the 25.10 client (https://github.com/flexcompute/compute/pull/6942). The benchmark reproducer notebooks pin older client families (25.8 / 25.9), so the helper has to be backported to those lines for the notebooks to run as-is.

Test Plan

• from flow360.examples import download_benchmark_assets imports cleanly.
• download_benchmark_assets("NACA_0012", "root_assets") returns the local mesh path from the public benchmark bucket.

🤖 Generated with Claude Code

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Note

Low Risk
Additive examples helper with no changes to core SDK paths; includes path-traversal checks on manifest entries before writing files.

Overview
Backports download_benchmark_assets onto the 25.9 client so benchmark reproducer notebooks can pull published case files without credentials or private project IDs.

Adds flow360/examples/benchmark_assets.py, which fetches from the public simcloud-public-1 benchmark bucket via stdlib urllib/json. Callers pass case_id and kind (root_assets for geometry/mesh snapshots, or folders like ref_data); multi-project cases can pass project_id. Downloads honor manifest layout (flat under to_folder for root assets, to_folder/<kind>/… for input data) and reject manifest paths that escape the destination root.

flow360.examples re-exports the helper in __all__ for from flow360.examples import download_benchmark_assets.

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