Add AutoCAD DXF data source

[ghanse]

Changes

This PR introduces the following changes:

• Implements a PySpark Python Data Source for reading AutoCAD DXF files using the ezdxf library
• Extracts geometric entities (LINE, CIRCLE, ARC, TEXT, LWPOLYLINE, ELLIPSE, SPLINE, INSERT, POLYLINE, MTEXT, DIMENSION, HATCH, POINT) into a tabular schema with file_path, entity_type, layer, handle, and attributes (JSON) columns
• Supports layerFilter option for read-time layer filtering, recursiveFileLookup, configurable numPartitions, and pathGlobFilter
• Includes 13 unit tests covering path handling, entity extraction, attribute parsing, layer filtering, and partition logic
• Adds sample DXF test fixture, README, Makefile, and requirements.txt

To-Do

• Update the implementation based on changes in Update repo structure and build tooling #17