Hatching algorithm and AI coding

Hi,

I have been trying AI coding with the recent PR: https://github.com/LibreCAD/LibreCAD/issues/2280

The PR introduces a new hatching algorithm based on topology algorithms. This is needed as the legacy algorithm is poor on topology analysis, and causing many hatching/solid fill issues.

The AI code is not really following our coding style yet, but the algorithm appears to be working after a few attempts.

The success makes it's conceivable to finish the long requested features:

1. hatching by clicking on an enclosed area;
2. Updated DWG support; probably also add a dwg2dxf tool (in addition to dxf2pdf and dxf2png).

I have been trying DeepSeek (as it's free) and Grok-4 (this one costs a few hundred dollars per year).