Measturement: Area measurement from edges

### Problem description

Add area measurement to group of line segments. While trying to measure slots on this part I had to measure the internal surface area without the slots and then with them to find the total slot area (see spreadsheet in file). The slots were created with the pocket tool and an offset plane, so I could not use the internal faces generated by a sketch.

[FreezeGuard.zip](https://github.com/user-attachments/files/29762921/FreezeGuard.zip)

### Workbench affected?

Measurement

### Steps to reproduce

Create any 3d object or sketch.
Select multiple intersecting lines my holding ctrl and click each line.
Select the measurement tool and change the mode to Area.

### Expected behavior

I would expect it to display the area similar to when you measure a face of a 3d object or internal faces on sketches if enabled.

### Actual behavior

No area is displayed.

### Development version About Info (in Safe Mode)

```shell
OS: Windows 11 build 26100
Architecture: x86_64
Version: 26.3.0dev.20260630 (Git shallow)
Build date: 2026/06/30 20:58:37
Build type: Release
Branch: (HEAD detached at ba406c730)
Hash: ba406c730396ec276004d5ef6c70d96a5a97488b
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, Clipper2 , IfcOpenShell 0.8.2, OCC 7.8.1
Locale: English/United States (en_US) [ OS: English/United States (en_US) ]
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Navigation Style/Orbit Style/Rotation Mode: Revit/Rounded Arcball/Window center
Logical DPI/Physical DPI/Pixel Ratio: 96/113.268/1.25
```

### Last known good version (optional)

```shell

```

Reproduce the issue in the Measurement workbench using a 3D object or sketch, selecting multiple intersecting lines and switching the measurement tool to Area. Start by tracing the measurement tool's Area mode and its handling of selected edges. Done means the tool displays the enclosed area for a group of intersecting line segments, comparable to face measurement.

Written by the indexing model from the issue text.