Fix Pixie binding ABI value types

[treeform]

Summary

• Mark custom vector and matrix binding structs as C by-value types
• Export Typeface rune APIs with C-safe integer parameters

Verification

• nim c --mm:arc --app:lib -d:gennyZig --path:../genny/src --path:src -o:bindings/generated/pixie.dll bindings/bindings.nim