Track Tinker cookbook checkpoint compatibility limitations

[ShubyM]

Open-RL can run the Tinker cookbook recipe loops against local endpoints, but durable checkpoint compatibility is still limited.

Current limitation:

• Cookbook recipes that expose periodic durable checkpoint saves should run with save_every=0 for now.
• Sampler refreshes through save_weights_and_get_sampling_client are still supported.
• Full Tinker-compatible checkpoint listing/download/restore semantics should be tracked separately from the recipe guide.