fix(ci): reuse unchanged test images

[zhangyue207]

Summary

• Pin InfiniOps workflows to a new reusable CI revision that uses content-based test image tags.
• Reuse an existing local test image when the platform Dockerfile context and image build config have not changed.

Validation

• python -m pytest tests/test_build.py tests/test_workflow.py tests/test_shadow_workflow.py tests/test_workflows.py -q in .ci
• python -m py_compile build.py run.py config_to_matrix.py in .ci
• git diff --check

[zhangyue207]

Superseded by #625.