Revert "feat: implement temporary code freeze with core-platform as sole CODEOWNERS" (#6960)

Reverts #6947

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Restores detailed CODEOWNERS mappings and re-enables codeowner
validation in Yarn constraints.
> 
> - **Repo governance**:
> - Restore detailed CODEOWNERS rules per team and package; add
ownership for `.github/` to `@MetaMask/core-platform`.
> - **Tooling (Yarn constraints)**:
>   - Re-enable `expectCodeowner` check for child workspaces.
> - Reintroduce `cachedCodeownersFile` and full `expectCodeowner`
implementation to validate package-level rules and core-platform
co-ownership of `CHANGELOG.md` and `package.json`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
8dd34e9. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Mark Stacey <[email protected]>

Author: cryptodev-2s