Module prelude

Auto-imported prelude of commonly-used stdlib items.

Re-exports core numeric aliases, foundational traits, collection protocols, iterator types, AST types, and the format macro so user code sees them without explicit :use. Enum and union variants (false, true, None, Some, Ok, Err, …) come automatically when their parent type is imported.

Deliberately omitted:

• Reflection (:type-info, the Reflect trait, type-info records) — users :use silo:std.reflection explicitly.
• HashMap / HashSet, the BTree / VecDeque / LinkedList / BinaryHeap types, sync primitives (Mutex, RwLock, Atomic, Lazy), and IO traits (Read / Write / BufRead / Seek) — users :use the owning module directly.

Several planned items (I128, U128, USize, ISize, Num, Integral, Neg, vec/1..vec/16, unwrap-or-default, checked/wrapping operator variants, format-args / parse macros) land once their backing implementations do.