chore: updates needed for compatibility with nfts in the tui

[pauldelucia]

Issue being fixed or feature implemented

Some files of the SDK were not public so they couldn't be accessed from the TUI where they are needed.

I also derived Serialize and Deserialize for the Index struct because I need to serialize the data contract indexes in order to display them in the TUI.

I also changed an error message to display more info, and made it a String instead of a str. The rest of the error messages should be changed to a String as well in a separate PR (#1839)

What was done?

See above.

How Has This Been Tested?

Works in the TUI and passes tests

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[qwizzie]

Does this affect Dash Platform stability testing (iaw your guide), through use of Platform TUI ? Should we wait on the merger of this pull request ?

Edit : or is the relevant part possibly affecting Platform stability testing already merged through pull request 1832 ?

[pauldelucia]

Does this affect Dash Platform stability testing (iaw your guide), through use of Platform TUI ? Should we wait on the merger of this pull request ?

Edit : or is the relevant part possibly affecting Platform stability testing already merged through pull request 1832 ?

@qwizzie this will just allow for the NFT-related state transitions to be used in the TUI, both in the strategy tests once I add them, and also just in the Contracts screen.