[export] Add backwards compatibility tests for v6.

[gnecula]

The serialization version v6 was introduced in #33597.
I have tested these manually for forward compatibility by
cherry-picking this PR on a version of the code before v6.

[gemini-code-assist]

Summary of Changes

Hello @gnecula, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the robustness of JAX's export serialization by adding comprehensive backwards compatibility tests for serialization version 6. It ensures that exported JAX functions, particularly those dealing with memory space and sharding configurations, can be reliably deserialized and executed across different versions. The changes involve introducing new test data and refining the testing utilities to support these validations.

Highlights

• New Backwards Compatibility Test Data: Added export_with_memory_space.py to store serialization data for JAX's export feature, specifically for functions involving memory space.
• Updated Existing Test Data: Existing test data files (export_with_specified_sharding.py, export_with_unspecified_sharding.py) were updated to include serialization data for version 6, ensuring compatibility with the latest serialization format.
• Enhanced Serialization Test Utility: The export_and_serialize helper function now supports specifying target platforms during export and generates cleaner output filenames for test data.
• New Test Case for Memory Space: A new test test_with_memory_space was introduced to validate the correct serialization and deserialization of JAX functions that utilize specific memory spaces (e.g., "pinned_host").

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[gemini-code-assist]

Code Review

This pull request adds backward compatibility tests for serialization version 6. The changes include a new test for memory_space serialization, along with the corresponding test data for versions 5 and 6. Existing test data files for sharding are also updated with version 6 data. The test helper export_and_serialize is updated to support platforms and to generate cleaner filenames for new test data. The changes are well-structured, correct, and follow existing patterns in the codebase. I have no specific comments for changes.

[mwhittaker]

Nice!