Support subtype INTERNAL fields

[Sean-Kenneth-Doherty]

Summary

• let each selected B9 subtype provide its own nested INTERNAL values for Reviva's runtime part config
• keep the runtime INTERNAL name synchronized with the selected subtype
• document how subtype authors can provide fields such as offset for part/internal relationships that need them

Fixes #35.

Validation

• git diff --check
• dotnet build Reviva.sln -c Release --no-restore /p:KSPRoot="/home/sean/.local/share/Steam/steamapps/common/Kerbal Space Program": 0 warnings, 0 errors

Caveat

I have not run an in-game shuttle runtime test, so this remains a draft for maintainer review.

[JonnyOThan]

This isn’t the correct solution, because it would apply the same offset fields to all of the different internals. The offset/scale parameters are inherent to the relationship between the part and one specific internal space.

[Sean-Kenneth-Doherty]

You're right. Copying the existing part INTERNAL node would apply one part/internal relationship to unrelated IVA selections.

I've replaced that with a narrower approach: Reviva now creates a fresh runtime INTERNAL node, sets the selected internal name, and only copies extra fields from an INTERNAL node nested in that specific subtype's ModuleIVASwitch data. I also added README guidance for configs that need an offset or similar per-subtype field. Build is still clean against the local KSP 1.12.5 setup.