Rust code generation from type-checked Assura contracts.
Takes a TypedFile from assura-types and generates a Rust project
consisting of a Cargo.toml and one or more .rs source files.
Generated Rust is formatted via prettyplease.
This is T019: the initial scaffolding. Type mapping (T020), contract codegen (T021), project generation (T022), and struct/enum codegen (T023) extend this foundation.