chore: create new assets controller package

[salimtb]

Explanation

This PR introduces a new @metamask/assets-controller package as a placeholder for future consolidation of asset tracking functionality.

Current state:
Asset tracking functionality (account balances, token balances, asset detection) is currently spread across multiple controllers in the @metamask/assets-controllers package.

Solution:
This PR creates an empty @metamask/assets-controller package as a foundation for future work to consolidate asset tracking into a single, unified controller. The package currently exports nothing and serves as a placeholder with TODOs indicating the intended scope:

• Account balance tracking
• Token balance tracking
• Asset detection

No functional changes are included in this PR.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

---

Note

Introduces a new placeholder package for future asset tracking consolidation.

• Adds @metamask/assets-controller with a minimal AssetsController (empty state), exports, unit tests, README, LICENSE, CHANGELOG, Jest/TypeDoc/TS configs, and build scripts
• Updates monorepo wiring: adds package to README (list + graph), CODEOWNERS, teams.json, root tsconfig.json and tsconfig.build.json references, and yarn.lock entry

^{Written by Cursor Bugbot for commit a0bae1b. This will update automatically on new commits. Configure here.}

[mcmire]

Two questions:

1. What do you think about copying and pasting one of the controllers in the sample-controllers package? This way we can keep the general look and feel for a controller consistent across all packages.

2. I see that we are creating a new package called assets-controller, when we already have a package called assets-controllers (with an "s"). I'm a bit worried this will be a constant source of confusion, and so perhaps we shouldn't make a new package yet? Or — are there any near-term plans to split apart assets-controllers?

[salimtb]

@mcmire yes, there are near-term plans to split apart assets-controllers. The goal is to deprecate the existing assets-controllers (plural) package and break it into several focused, single-responsibility packages:

• @metamask/assets-controller - consolidated asset tracking (balances, detection)
• Other controllers from the package will be split into their own dedicated packages as well

The naming is intentional:

• assets-controllers = legacy "kitchen sink" package (to be deprecated)
• assets-controller = new single unified controller

This follows the pattern we've used elsewhere in the monorepo where packages contain a single controller (e.g., @metamask/network-controller, @metamask/keyring-controller).

Once the migration is complete and assets-controllers is deprecated and deleted, the confusion will be resolved. In the meantime, we can add a note to the assets-controllers README indicating it's being deprecated and pointing to the new packages.

[mcmire]

@salimtb Okay, that sounds like a great plan. Thanks for clarifying!