Fix schema check and update import paths

- Use `collect_schema` for accurate column validation in Polars and
  correct
  relative import paths for statistical modules.

stats/correlation.py

@@ -9,8 +9,8 @@ import numpy as np
 import pandas as pd
 import plotly.graph_objects as go
 
-from utils.extractor import load_data
-from utils.extractor import to_int
+from stats.utils.extractor import load_data
+from stats.utils.extractor import to_int
 
 def _format_can_id_vec(s: pd.Series) -> pd.Series:
     s = s.astype('string').str.strip()