spawnManager

pub fn spawnManager(
    wg: *WaitGroup,
    comptime func: anytype,
    args: anytype,
) void {
    if (builtin.single_threaded) {
        @call(.auto, func, args);
        return;
    }
    const Manager = struct {
        fn run(wg_inner: *WaitGroup, args_inner: @TypeOf(args)) void {
            defer wg_inner.finish();
            @call(.auto, func, args_inner);
        }
    };
    wg.start();
    const t = std.Thread.spawn(.{}, Manager.run, .{ wg, args }) catch return Manager.run(wg, args);
    t.detach();
}