cad/openvsp: Update to 3.51.3

ChangeLog: https://openvsp.org/blogs/announcements/2026/08/17/openvsp-3-51-3-released

Features:

• API code examples now serve as unit tests
• AI Audit for API completeness
• VSPAERO Outputs more stuff for dynamic analysis

Build System:

• Update AngelScript to v2.38
• Improve Python MANIFEST.in and packaging

Bugs:

• Fix AngelScript registration of vec3d and Matrix4d
• Fix thin shell inertia calculation
• Fix many small bugs identified by new unit tests
• Fix matrix spreadsheet UI referencing
• Fix DeltaFlatPlateDragArea for unsteady cases (thanks Jaime)
• Swept_Wing_API example VSPAERO script brought current (thanks Roman)