101 wip for as template effect

// `for` as a void effect pump: `! each` fires per iteration, NO terminal branch
// (no `| done`, no count — that would be pay-for-nothing on every loop). The
// iterable is template-substituted into the Zig `for`; the body calls the
// `! each` handler symbol. This is the real shape of the `for` we're building —
// 400_071 (effect_branch_multifire_void) proves the void-pump shape works; the
// only delta here is the templated iterable.
~import std/io

~pub event loop { r: i32 }
! each usize

~proc loop|template|zig {
    for ({{ r }}) |item| {
        each(item);
    }
}

~loop(r: 0..3)
! each v |> std/io:print.blk {
    v {{ v:d }}
}