Remove toolkit_legacy.py and references to it

src/sp2xr/__init__.py

@@ -1,16 +1 @@
-"""
-Thin wrapper so `import sp2xr` keeps working
-while we refactor the legacy monolith.
-"""
-
-from importlib import import_module
-
-# 1 Load the legacy monolith (makes old symbols available)
-_toolkit = import_module(".toolkit_legacy", package=__name__)
-globals().update(_toolkit.__dict__)  # re‑export legacy names
-
-# 2 Import new helpers you want public at package root
-from .io import csv_to_parquet, process_sp2xr_file  # noqa: F401,E402
-
-# Cleanup internal names
-del import_module, _toolkit
+"""SP2XR - Single Particle Soot Photometer Extended Range Toolkit"""

src/sp2xr/io.py

@@ -11,8 +11,12 @@ import numpy as np
 import dask.dataframe as dd
 import logging
 
-from .toolkit_legacy import calculate_delta_sec, extract_datetime
-from .helpers import find_matching_hk_file, extract_sp2xr_filename_parts
+from .helpers import (
+    find_matching_hk_file,
+    extract_sp2xr_filename_parts,
+    calculate_delta_sec,
+    extract_datetime,
+)
 
 logger = logging.getLogger(__name__)
 logger.setLevel(logging.INFO)