refactor: Unflatten MetamaskController stores (1/5)

[MajorLift]

Important

CI fails will be addressed in subsequent PRs. Review on high-level approach needed first.

Motivation

Eliminates flattening operation performed on the background state proxy object before it's supplied to the Redux store.

• Better debugging: Removes unnecessary obfuscation on which state property belongs to which controller, making runtime error messages easier to understand.
• Reduces errors: By isolating each controller's state in Redux, the possibility of state pollution due to one controller overriding state properties that belong to another controller is removed.
• Performance optimization for UI startup and state updates via patch generation.

Description

The key changes are in the following files:

• app/scripts/metamask-controller.js
• shared/types/metamask.ts
• app/scripts/lib/PatchStore.ts
• app/scripts/lib/ComposableObservableStore.js -> app/scripts/lib/ComposableObservableStore.ts

Note

See PR comments below for a walkthrough of the changes.

Related issues

• 1/5 PRs that will close https://github.com/MetaMask/MetaMask-planning/issues/2894
  • The CI run for this PR will not pass until all PRs in this ticket are completed.
• Blocked by:
  • fix: Move foreground state properties from metamask slice to appState slice #28703
  • chore: Bump reselect to ^5.1.1 for heterogenously-typed selectors support #29094
  • fix: Bridge{,Status}Controller state types and restricted-path imports #28971

Manual testing steps

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

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