## Summary
- add Divan benchmarks for prompt image re-encoding paths
- wire the image benchmark smoke test into Rust CI workflows
## Why
Image prompt handling includes re-encoding work that benefits from
repeatable benchmark coverage so changes can be measured in CI and
locally.
This already helped identify a potential regression from changing compiler flags.
## Impact
Developers can run and compare the new image re-encoding benchmarks, and
CI exercises the benchmark target via the Rust benchmark smoke test.
Adam Perry @ OpenAI