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/preprocess.py

@@ -2,7 +2,6 @@
 
 import click
 
-from astrai import setup_logging
 from astrai.config.preprocess_config import PipelineConfig
 from astrai.preprocessing.pipeline import Pipeline
 
@@ -48,5 +47,4 @@ def preprocess_command(inputs, output_dir, pipeline_config, tokenizer_path, batc
 
 
 if __name__ == "__main__":
-    setup_logging()
     preprocess_command()