shift int/uint tests around to avoid code repetition

[glacjay]

fix issue #22535

[rust-highfive]

r? @aturon

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[aturon]

Thanks for the PR! This looks basically good, but I wonder if the tests would be better placed in num itself? It's a bit arbitrary to plop them in usize.

[glacjay]

@aturon Thanks for your review.

I just choose a most possible place in my opinion, because this tests are all for unsigned types. Should I move them to src/libstd/num/mod.rs or not?

[glacjay]

@aturon I've just found that put mod tests in usize.rs will trigger "duplicate definition of type or module tests" error. I'll move tests to mod.rs, as you said, and submit a new PR.