Run submission runner tests in CI

[mrhimanshu]

Summary

• restore submission runner tests after the algorithm and workload registry moves
• update the MNIST JAX development submission to the current global-sharding model
• pin a TensorFlow Metadata version compatible with the existing Protobuf constraint
• run the restored JAX and PyTorch end-to-end tests in the pytest CI job

Closes #865

Testing

• python -m pytest tests/submission_runner_test.py -q (3 passed)
• python -m pytest tests/test_version.py tests/test_ssim.py -q (7 passed)
• python -m ruff check on changed Python files
• python -m ruff format --check on changed Python files
• dependency compatibility check and TOML/YAML parsing

[github-actions]

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[mrhimanshu]

recheck