Add new `geo-traits` crate

[frewsxcv]

• [ ] I agree to follow the project's code of conduct.
• [ ] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

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See https://github.com/georust/geo/pull/1011. We can use this draft pull request to view the changes from the work-in-progress traits branch.

[JasmineLowen]

Just a comment: I think the name of the crate is a bit confusing. Since geo relies on the num crate quiet heavily I thought the new geo-traits crate was similar to the num-traits crate which separates all the traits one can find in num nicely so we don't have to pull in all of num everywhere.

However, it seems that geo-traits implements entirely new traits instead.

I was just looking for a lightweight way to get the HasKernel trait which is required for a data type I'm defining in a separate crate for use everywhere else

[frewsxcv]

Closing in favor of https://github.com/georust/geo/pull/1157