Refactor: Reorganize root utilities into subdirectories

Structure changes:
  DataFrameUtils.py → dataframe_utils/DataFrameUtils.py
  FormulaLinearModel.py → formula_utils/FormulaLinearModel.py

New packages:
  - dataframe_utils: Plotting and statistics utilities
  - formula_utils: Formula-based modeling with code export

Fixes:
  - Removed self-import bug in FormulaLinearModel.py
  - Updated main __init__.py exports
  - Added package __init__.py files

Backward compatibility maintained via main __init__.py.
All imports working ✅

Author: miranov25

UTILS/dfextensions/DataFrameUtils.py …nsions/dataframe_utils/DataFrameUtils.pyUTILS/dfextensions/DataFrameUtils.py renamed to UTILS/dfextensions/dataframe_utils/DataFrameUtils.py UTILS/dfextensions/DataFrameUtils.py renamed to UTILS/dfextensions/dataframe_utils/DataFrameUtils.py

@@ -0,0 +1,9 @@
+"""
+DataFrame utilities package.
+
+Provides plotting and statistics utilities for DataFrames.
+"""
+
+from .DataFrameUtils import *
+
+__version__ = '1.0.0'

UTILS/dfextensions/dataframe_utils/__init__.py

@@ -0,0 +1,10 @@
+"""
+Formula utilities package.
+
+Provides formula-based linear modeling with code export capabilities.
+"""
+
+from .FormulaLinearModel import FormulaLinearModel
+
+__all__ = ['FormulaLinearModel']
+__version__ = '1.0.0'