Introduce the AssetId type

[SwayStar123]

Description

Change AssetId from alias to struct. Allows implementing of methods. Also moved the helper functions into the struct as methods.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[bitzoic]

This is a non-trivial change and involves breaking changes to existing libraries, applications, the rust SDK, the typescript SDK, and the indexer.

[SwayStar123]

contract id needs to import asset id and assetid needs to import contract id, rip lol

[Braqzen]

@bitzoic has recently raised an issue for the keccak256 hashing so I guess we can leave it for that instead of this PR

[anton-trunov]

There is a bunch of lines like this one:

        let asset_id = sha256((contract_id(), ZERO_B256));

in test/src/sdk-harness/test_artifacts/context_caller_contract/src/main.sw

I'm not sure if it's related to this PR or not.