096 effect branch void payload

// Test: void-payload effect branch — `! pong` declared with no payload type,
// producer calls `pong()` with no args, consumer handles with `! pong |>` (no
// binding). Mirrors the vaxis `! ready` shape — an effect that fires for the
// fact of firing, with no information to carry.
//
// A terminal `| result i32` is included because a single void-payload effect
// with no terminal is rejected by PARSE003 (a single no-payload branch is
// redundant — you could just call the proc directly).

~import std/io

~pub event ping {}
! pong
| result i32

~proc ping|zig {
    pong();
    return .{ .result = 1 };
}

~ping()
! pong |> std/io:print.ln("pong")
| result n |> std/io:print.blk {
    result {{ n:d }}
}