Add adapter upload configuration support

[JannikSt]

Summary

• Add AdaptersConfig class with interval and keep_last settings
• Add adapters_config parameter to create_run API
• Update config template with [adapters] section

Config Example

[adapters]
interval = 100  # Upload adapter every 100 steps (0 = only at run end)
keep_last = 3   # Keep 3 adapters in cloud (-1 = keep all)

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Note

Low Risk
Additive, optional CLI/API payload fields to configure adapter uploads; main risk is backend schema mismatch if the new adapters payload is not supported.

Overview
Adds optional adapter upload configuration for hosted RL runs via a new [adapters] block (with interval and keep_last) in the generated RL TOML template.

Plumbs this config through the CLI into the API: introduces AdaptersConfig on RLConfig, passes adapters_config to RLClient.create_run, and includes an adapters object in the /rft/runs create-run payload when provided.

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