Transpiler: closure structs from local functions capturing byte[] arrays

[jonathanpeppers]

Follow-up from PR #211 (crypto.c sample port).

When local functions in top-level statements reference outer byte[] variables, the C# compiler generates closure structs. The transpiler fails with:

System.InvalidOperationException: Cannot resolve struct type for local 0 with field 'palette'

Root cause

In C# top-level statements, all defined functions are local functions of the implicit Main method. When any local function references a byte[] array from the outer scope, the compiler wraps captured variables in a display class. The transpiler encounters stfld/ldfld on this compiler-generated struct and fails.

Workaround

1. Inline all capturing functions into the main body (eliminates closures but loses abstraction)
2. Convert to partial class methods with byte[] parameters (works for functions with few captures)
3. Use const values instead of byte[] where possible (consts are compile-time inlined, no closure)

Long-term fix

Either teach the transpiler to handle compiler-generated closure types, or provide guidance to users to structure code to avoid closures (e.g., use partial class Program methods with parameters).