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/generate.py

@@ -6,7 +6,6 @@ import click
 import torch
 from tqdm import tqdm
 
-from astrai import setup_logging
 from astrai.inference import InferenceEngine
 from astrai.model import AutoModel
 from astrai.tokenize import AutoTokenizer
@@ -157,5 +156,4 @@ def generate_command(**kwargs):
 
 
 if __name__ == "__main__":
-    setup_logging()
     generate_command()