Split ml-rl into ml-dqn and ml-ppo for 3-way parallel compilation
and better sccache hit rate. Extract TradingAction to ml-core to
enable full DQN/PPO independence.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Split the monolithic ml crate (260K lines, 55s compile) into 5 crates:
ml-core, ml-rl, ml-supervised, ml-infra, ml (facade).
15-task plan with full module inventory and import migration guide.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>