[PROTOTYPE] Unified save/load

[jlamypoirier]

✨ Description

Please provide a brief summary of the changes, relevant motivation, and context.
Include any related issue numbers or links to discussions, and explain why this change is necessary.

Closes #

🔍 Type of change

Select all that apply:

• [ ] 🐛 Bug fix (non-breaking change that addresses a specific issue)
• [ ] 🚀 New feature (non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (a change that could affect existing functionality)
• [ ] 📈 Performance improvement/optimization (improves speed, memory usage, or efficiency)
• [ ] 🛠️ Code refactor (non-functional changes that improve code readability, structure, etc.)
• [ ] 📦 Dependency bump (updates dependencies, including Dockerfile or package changes)
• [ ] 📝 Documentation change (updates documentation, including new content or typo fixes)
• [ ] 🔧 Infrastructure/Build change (affects build process, CI/CD, or dependencies)

📝 Changes

List the key changes introduced in this PR:

1. Change A
2. Change B

✅ Checklist

Make sure the following tasks are completed before submitting the PR:

General:

• [ ] 📜 I have read and followed the contributing guidelines.
• [ ] 🎉 The functionality is complete, and I have tested the changes.
• [ ] 📝 I have updated the documentation if needed.
• [ ] ⚠️ The change does not introduce any new issues (e.g., runtime warnings, type checker errors, linting problems, unhandled edge cases).
• [ ] 🧩 I have commented my code, especially in hard-to-understand areas.

Dependencies and Configuration:

• [ ] 🐋 I have updated the Docker configuration or dependencies, if applicable.
• [ ] 🔄 I have ensured compatibility with the existing setup after dependency changes.

Testing:

• [ ] 🧪 I have added or updated tests to cover my changes.
• [ ] ✔️ New and existing tests pass locally with my changes.
• [ ] 🚦 I have tested these changes on GPUs and verified training stability.
• [ ] 🏋️ I have tested the changes on realistic training workloads, if applicable.

Performance Impact:

• [ ] 📊 I have run benchmarks where applicable to evaluate the performance impact.
• [ ] ✅ The benchmarks show no performance regression.
• [ ] 🚀 The benchmarks indicate a potential performance improvement.
• [ ] ⚠️ The benchmarks indicate a potential performance degradation.
• [ ] 📈 I have provided benchmark results and detailed any performance impact below, if applicable.

📊 Performance Impact Details

If there is any impact on performance, describe it and provide benchmark results, if applicable:

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📝 Additional Notes

Include any additional context, information, or considerations here, such as known issues, follow-up tasks, or backward compatibility concerns.