feat: Add W&B run config API

[vivekkalyan]

Summary

• add a public Model.update_wandb_config() API for attaching run config to ART-managed W&B runs
• seed config at wandb.init(...) and sync it onto active runs without exposing mutable-config semantics
• reject conflicting updates so run config stays immutable once set
• add unit coverage for init-time config logging, active-run sync, and conflict rejection

Testing

• uv run pytest tests/unit/test_metric_routing.py -q
• uv run pytest tests/unit/test_frontend_logging.py -q
• uv run ruff check src/art/model.py tests/unit/test_metric_routing.py
• uv run ruff format --check src/art/model.py tests/unit/test_metric_routing.py

Downstream verification

• pointed at this branch locally
• logged a sanitized training config through ART and verified it appeared on the W&B run config