Ilya/fireworks cookbook resume fixes

[shfunc]

Note

Medium Risk
Resume changes training client setup and when tokenizer/renderer load; wrong flags on non-default checkpoints could fail or mis-tokenize before training starts.

Overview
Resume and model resolution for the Fireworks RL cookbook: --resume-from now looks up the checkpoint’s base model via the Fireworks REST API and overrides CLI --base-model before tokenizer/renderer setup. Non-default models must pass both --tokenizer-model and --renderer (defaults apply only for Qwen 3.8 27B). The startup banner and config.json record the resolved model, tokenizer, and renderer.

Checkpoint visibility: each state-NNNN and final-state save prints Training checkpoint: <full path> immediately so paths are available even if a later step fails.

Tests and docs: new unit tests cover resume model override, missing rendering args on alternate bases, and checkpoint logging before failures; README and v6 cookbook docs describe the updated resume flow and CLI help.

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