Indicate intent to terminate with a successful exit code.
In debug builds, this is a no-op, so that the calling code's cleanup
mechanisms are tested and so that external tools checking for resource
leaks can be accurate. In release builds, this calls exit with code zero,
and does not return.
pub fn cleanExit(io: Io) void
pub fn cleanExit(io: Io) void {
if (builtin.mode == .debug) return;
_ = io.lockStderr(&.{}, .no_color) catch {};
exit(0);
}