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 monorepo package @metamask/assets-controller as a scaffold for future asset tracking consolidation.

• Adds AssetsController (BaseController-based) with empty state, getState action, and stateChange event typing; exports via src/index.ts
• Includes tests (AssetsController.test.ts) validating default state, action wiring, and event subscription
• Adds package scaffolding: package.json, tsconfigs, Jest config, Typedoc, README, LICENSE
• Wires package into repo: updates README (package list + graph), .github/CODEOWNERS, teams.json, root tsconfig*, and yarn.lock

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[mcmire]

Can we use satisfies instead of a type assertion here? See SamplePetnamesController in the sample-controllers package:

core/packages/sample-controllers/src/sample-petnames-controller.ts

Lines 42 to 49 in 5db273f

	const samplePetnamesControllerMetadata = {
	namesByChainIdAndAddress: {
	includeInDebugSnapshot: false,
	includeInStateLogs: true,
	persist: true,
	usedInUi: true,
	},
	} satisfies StateMetadata<SamplePetnamesControllerState>;

Suggested change

	const assetsControllerMetadata: StateMetadata<AssetsControllerState> = {};
	const assetsControllerMetadata = {} satisfies StateMetadata<AssetsControllerState>;

[mcmire]

Generally we do not export names of controllers, controllerName is an internal variable only. If there are multiple controllers in a package then there would be multiple controllerName exports. Would you mind removing this?

Suggested change

controllerName,

[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?