feat(model): add TimeGAN components with LOB-aware scaffolding (Encoder/Recovery/Generator/Supervisor/Discriminator)

Implements GRU-based components with Xavier/orthogonal init, device/seed helpers, and typed handles. Sets BCEWithLogits-ready Discriminator and sigmoid-gated projections elsewhere. Preps for optional TemporalBackbone injection via config.

Author: keys-i