Removed 3 duplicate ModelType enums (model_loader, hyperopt campaign,
job_spawner). Canonical definition in ml/src/lib.rs with 15 variants.
model_loader and job_spawner now re-export from ml. Added as_str(),
s3_prefix(), Display, to_db_string(), and weight() to canonical enum.
Replaced conflicting ToString impl with Display. Fixed variant name
mismatches (Dqn->DQN, Mamba2->MAMBA, Liquid->LNN, TlobTransformer->TLOB).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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