feat: token version

[peterpeterparker]

Motivation

Because the UI/UX of custom tokens revolves around enabling and disabling tokens, I think it is worth adding a timestamp (UPDATE: replaced by a version counter following review) to the information to prevent use cases where the user operates on multiple devices simultaneously and would overwrite changes made on one device with those from another.

It may be a not-too-frequent scenario but, given that we are developing this new feature which is not yet live, I think it is the right time to add these kinds of assertions.

That's why this PR adds a version: Option<u64> to the existing UserTokens and CustomTokens.

Notes

In this PR, we are adding new information within a struct of stable memory that already exists on mainnet but, given that we introduce it as an option, it should be backward compatible. There is also a test about it.

Given that the backend sets the version when the entity is saved, it would be handy to return the new entity when setter and add functions are called. However, the Oisy frontend does not currently require it as we are reloading all the user tokens after changes. Therefore, this PR does not change those functions' returns.

For backwards compatibility, I did not modified the existing remove_from_user_token function which accept an ID.

Did files will be updated in a separate PR that also adapts the frontend code.

[bitdivine]

Suggestion:

If you add these traits to UserToken:

    #[derive(CandidType, Deserialize, Clone, Debug, Eq, PartialEq)]
    pub struct UserToken {

you can do assert_eq!(&one_token_list, &another_token_list, "My lists aren't the same!") without needing a dedicated comparison function.

If the default definition of Eq does not suit, it is possible to define a custom one.

[peterpeterparker]

Sure we can do that in another PR. Original did not wanted to change the existing struct but, we are passed that now ;)

[peterpeterparker]

Printing out the token in the assertions of the test requires implementing display. I don't think that's part of this PR, so I've reverted printing out and we can do that in another PR.

error[E0277]: `T` doesn't implement `std::fmt::Display`
  --> src/backend/tests/it/utils/assertion.rs:33:80
   |
33 |         assert!(token.get_timestamp().is_some(), "Token has no timestamp: {}", token);
   |                                                                                ^^^^^ `T` cannot be formatted with the default formatter
   |
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = note: this error originates in the macro `$crate::const_format_args` which comes from the expansion of the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting this bound
   |
30 |     T: TokenTimestamp + std::fmt::Display,
   |                       +++++++++++++++++++

[bitdivine]

LGTM. Thanks!