message: lib.rs: Simplify cfg_attr
diff: #![feature(is_some_and)]
  #![no_std]
  #![cfg_attr(target_os = "none", feature(custom_test_frameworks))]
  -#![cfg_attr(target_os = "none", cfg_attr(test, test_runner(crate::test_runner)))]
  +#![cfg_attr(all(target_os = "none", test), test_runner(crate::test_runner))]
  #![cfg_attr(
  - target_os = "none",
  - cfg_attr(test, reexport_test_harness_main = "test_main")
  + all(target_os = "none", test),
  + reexport_test_harness_main = "test_main"
  )]
  -#![cfg_attr(target_os = "none", cfg_attr(test, no_main))]
  +#![cfg_attr(all(target_os = "none", test), no_main)]
  #[cfg(all(feature = "newlib", feature = "pci"))]
  compile_error!("feature \"newlib\" and feature \"pci\" cannot be enabled at the same time");
  