Complete ACadSharp abstraction layer with full entity type coverage

[Copilot]

Implements ACadSharp adapter to enable runtime switching between netDxf and ACadSharp for DXF/DWG operations. Refactors ImportDxf to use abstraction interfaces, removing direct netDxf dependencies.

Implementation

ACadSharpLibraryAdapter (~900 lines)

• Entity adapters for 20+ types: Line, Arc, Circle, Ellipse, Spline, Polyline2D/3D, Text, MText, Hatch, Insert, Face3D, PolyfaceMesh, Mesh, Solid, Point, Ray, MLine, Dimension, Leader
• DXF and DWG file I/O using ACadSharp's DxfReader/DxfWriter and DwgReader/DwgWriter
• Color conversion from ACadSharp ACI to ARGB
• Block, layer, and linetype collection adapters

ImportDxf refactoring

• Converted 20 entity creation methods from netDxf.Entities.* to IDxf* interfaces
• Replaced Vector3 with tuple types (double X, double Y, double Z) for library neutrality
• Updated helper methods: GeoPoint, GeoVector, Plane, SetAttributes to use abstraction
• Layer/color mapping through abstraction layer lookups

Export extension

• Added IDxfEntityFactory interface with entity creation methods
• Implemented NetDxfEntityFactory and ACadSharpEntityFactory
• ExportDxf.cs continues using netDxf directly (export logic remains stable)

Usage

// Runtime library selection
var library = DxfLibraryFactory.GetLibrary(DxfLibraryType.ACadSharp);
var doc = library.LoadFromFile("drawing.dwg");

// Entity access through abstraction
foreach (var entity in doc.Entities)
{
    if (entity is IDxfLine line)
    {
        var (x1, y1, z1) = line.StartPoint;
        var (x2, y2, z2) = line.EndPoint;
    }
}

Architecture

Import/Export
    ↓
DxfLibraryFactory
    ↓
IDxfLibrary
   ├─ NetDxfLibraryAdapter (existing)
   └─ ACadSharpLibraryAdapter (new)

Enables DWG support via ACadSharp while maintaining netDxf compatibility for DXF workflows.

Original prompt

To fully migrate ImportDxf and ExportDxf to use the abstraction layer would require:
• Rewriting approximately 50 entity conversion methods in ImportDxf
• Rewriting approximately 30 entity export methods in ExportDxf
• Creating entity-level adapters or converters for each entity type

Please make sure that ACadSharp is fully implemented to support all types like lines, splines, etc...

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