work around sched_param having more members on some platforms

[nekopsykose]

closes #4

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i don't know how to write this without unsafe. normally Default::default() exists but it's not implemented in this case..

[nekopsykose]

technically, this is slightly incorrect because if the extra fields are actually used (outside of linux i guess lol), it would just setschedparam and overwrite the other fields with 0's. a correct solution would be to sched_getscheduler() first and change the priority on that object. but from what i can tell not everyone does that either for linux code:

• https://github.com/util-linux/util-linux/blob/f3fd64111c28de1ecd47f7cd519120ffa531800d/schedutils/chrt.c#L266
• https://github.com/systemd/systemd/blob/47174dc054619ae4fd6df7c9d76e37034fee518c/src/core/exec-invoke.c#L4236

a proper version would be

    let sched_param = unsafe {
        let mut param = std::mem::MaybeUninit::uninit();
        if -1 == libc::sched_getparam(0, param.as_mut_ptr()) {
            panic!("failed to sched_getparam");
        }
        (*param.as_mut_ptr()).sched_priority = 99;
        param.assume_init()
    };

these interfaces are 'fun'