"Refactor: Move AliasDataFrame to subdirectory

Structure:
- Move AliasDataFrame.py → AliasDataFrame/AliasDataFrame.py
- Move AliasDataFrameTest.py → AliasDataFrame/AliasDataFrameTest.py
- Add AliasDataFrame/__init__.py (maintains backward compatibility)
- Add AliasDataFrame/README.md
- Add AliasDataFrame/docs/ subdirectory
- Update dfextensions/__init__.py

Documentation:
- Add docs/COMPRESSION_GUIDE.md (comprehensive user guide)
- Add docs/CHANGELOG.md (version history)

Benefits:
- Consistent with other subprojects (groupby_regression/, quantile_fit_nd/)
- Self-contained subproject structure
- Clear documentation location
- Easy to add future features

Backward compatibility:
- All existing imports still work via updated __init__.py
- from dfextensions import AliasDataFrame
- from dfextensions.AliasDataFrame import CompressionState

Testing:
- All 61 tests still passing after restructure"

Author: miranov25

UTILS/dfextensions/AliasDataFrame/README.md

@@ -0,0 +1,41 @@
+# AliasDataFrame
+
+Lazy-evaluated DataFrame with bidirectional compression support for physics data analysis.
+
+## Features
+- Lazy evaluation via aliases
+- Bidirectional compression with state management
+- Sub-micrometer precision for spatial data
+- ROOT TTree export/import support
+- Incremental compression workflows
+
+## Quick Start
+```python
+from dfextensions import AliasDataFrame
+import numpy as np
+
+# Compress column
+adf = AliasDataFrame(df)
+spec = {
+'dy': {
+'compress': 'round(asinh(dy)*40)',
+'decompress': 'sinh(dy_c/40.)',
+'compressed_dtype': np.int16,
+'decompressed_dtype': np.float16
+}
+}
+adf.compress_columns(spec)
+```
+
+## Documentation
+- [Compression Guide](docs/COMPRESSION_GUIDE.md)
+- [Changelog](docs/CHANGELOG.md)
+
+## Testing
+```bash
+pytest AliasDataFrameTest.py -v
+# Expected: 61 tests passing
+```
+
+## Version
+1.1.0 - Selective Compression Mode

UTILS/dfextensions/__init__.py

@@ -4,16 +4,11 @@
 from .FormulaLinearModel import FormulaLinearModel
 from .DataFrameUtils import *  # if it provides general helper functions
 from .groupby_regression import *  # or other relevant functions
+from .AliasDataFrame import AliasDataFrame, CompressionState
 
 __all__ = [
     "AliasDataFrame",
     "FormulaLinearModel",
     "GroupByRegressor"
 ]
 
-
-try:
-    from .AliasDataFrame import AliasDataFrame
-    __all__.append("AliasDataFrame")
-except ImportError:
-    pass