136 effect arms never nest effects

// "Never nest `!`": an indented `!` under an effect branch is not a resume
// arm and not legal anywhere — effect composition lives in the flat `|` arm
// list, never in nested effects. Sibling of the accept pins 210_092/093.
~pub event request { payload: i32 }
! ask i32
    ! nested i32
    | timeout
| done i32

~proc request|zig {
    const r = ask(payload);
    return .{ .done = r };
}