feat(snap-account-service): add SnapAccountService

[ccharly]

Explanation

A new service where we will move the common logic of the current monolith SnapKeyring.

The idea is to be able to split this keyring into multiple ones and move the KeyringEvents logic in this service.

High-level architecture is the following:

For now, it's just an empty service, but we will move forward with more follow-up change as we are rewriting the existing SnapKeyring to use the new KeyringV2.

References

N/A

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

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Note

Low Risk
Low risk: this mainly introduces a new, currently-empty service package plus build/test/docs wiring, without changing existing runtime logic.

Overview
Introduces a new @metamask/snap-account-service package with an initial SnapAccountService class (messenger-namespaced, no exposed actions yet) and a basic init() plus a smoke test.

Wires the new package into monorepo metadata and tooling: adds it to the root README package list/dependency graph, TypeScript project references (tsconfig.json/tsconfig.build.json), CODEOWNERS/teams.json, and updates yarn.lock.

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[david0xd]

Can we have little bit more explanation here? For example, what is the main purpose of this service, what we should keep or implement here. So we build up some integrity of this package.

[david0xd]

When is this supposed to be implemented? Looks redundant at this moment.