Build submission zips from checkpoint bundles

[relh]

Summary

• Evaluator submission zip now built from checkpoint bundle paths.
• Avoid absolute data_path leaks in submission.zip.
• Update cogames run_evaluation to use policy_spec + safetensors.

Changes

• Evaluator reads policy_spec/data from bundle dir (local or S3) and rewrites absolute data_path if present.
• run_evaluation uses policy_spec_from_uri + safetensors.

Tests

• not run (stack recut)

[relh]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Update docs and recipes for checkpoint bundles #4468
• Move MptPolicy compatibility into metta #4467
• Build submission zips from checkpoint bundles #4466 👈 (View in Graphite)
• Adopt checkpoint bundles in training and losses #4465
• Resolve checkpoint bundle URIs and load specs #4464
• Add checkpoint bundle primitives #4463
• main

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