refactor: centralize logging in astrai.logging, replace ASTRAI_TIMED with log level

- move setup_logging to astrai/logging.py
- timed() now uses logger.isEnabledFor(DEBUG) instead of separate env var
- enable ASTR_LOG_LEVEL=DEBUG to see per-step timing logs
- call setup_logging() in stream_chat.py

scripts/tools/train.py

@@ -8,7 +8,6 @@ import torch
 from click.core import ParameterSource
 from torch import optim
 
-from astrai import setup_logging
 from astrai.config import AutoRegressiveLMConfig, TrainConfig
 from astrai.dataset import DatasetFactory, dpo_collate_fn, grpo_collate_fn
 from astrai.model import AutoRegressiveLM
@@ -828,5 +827,4 @@ def train(
 
 
 if __name__ == "__main__":
-    setup_logging()
     train_command()