Constructors and normalization for Rust type AST nodes.

type/1 accepts existing type nodes, atom/list Rust paths, raw binary source, and structural tuples such as {:option, type}, {:result, ok, error}, {:vec, type}, tuple types, references, slices, and arrays. Binary source is normalized to RustQ.Rust.AST.TypeRaw; prefer raw/1 when an explicit escape makes generator intent clearer.