Derive Copy and Hash for IntErrorKind

[ranger-ross]

This PR derives Copy and Hash for IntErrorKind to make it easier to work with. (see #131826)

I think an argument could be made to also derive PartialOrd + Ord as well given that other error kinds in the std like io::ErrorKind do this. Granted these seem much less useful for errors.

Fixes #131826

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[joboet]

Makes sense to me, but this will need FCP.
r? libs-api

[tgross35]

This is a pretty easy change, nominating to get it on the radar.

@rustbot label +I-libs-api-nominated

[m-ou-se]

@rfcbot merge

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Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members:

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[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.