rust: Implement Display instead of ToString for enums

[wiktor-k]

Rust docs for ToString explicitly recommend implementing Display:

This trait is automatically implemented for any type which implements the Display trait. As such, ToString shouldn’t be implemented directly: Display should be implemented instead, and you get the ToString implementation for free.

See: https://doc.rust-lang.org/std/string/trait.ToString.html
See: Nitrokey/nethsm-sdk-rs#33

Since this is about Rust, CC'ing @frol @farcaller @richardwhiuk @paladinzh @jacob-pro

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[wing328]

thanks for the PR

please follow step 3 to update the samples so that CI can test the change

[wiktor-k]

please follow step 3 to update the samples so that CI can test the change

Ugh, I created a commit and ran the instructions but didn't notice they change files 🤦‍♂️

I think it should be better now. Thanks for reviewing!

[wing328]

@wiktor-k thanks for updating the samples

is this a breaking change?

shall we keep the ToString method for backward compatibility and mark it as deprecated?

[wiktor-k]

is this a breaking change?

shall we keep the ToString method for backward compatibility and mark it as deprecated?

Hi!

No, this is not a breaking change since the Rust compiler will automatically add ToString using Display (as explained in the description from docs I quoted in the PR). (Technically it's not even possible to leave the old code as it will conflict with the auto-generated one).

This is strictly an extension of existing code. All previous code will compile without issues and it will enable new API functions.

Happy to answer further questions! 👋

[wing328]

thanks for the explanation.

will merge after all tests pass

(ciricleci failure can be ignored for the time being)