Upgrade @metamask/multichain-account-service to version 7.0.0

A new major version of `@metamask/multichain-account-service`, 7.0.0, is now available. This issue has been assigned to you and your team because you code-own this package in the `core` repo. If this package is present in this project, please prioritize upgrading it soon to unblock new features and bugfixes.

Search the repository for references to @metamask/multichain-account-service and identify whether it is present as a dependency. Update the package reference to version 7.0.0, then run the relevant project checks; done means the dependency is upgraded without introducing failures.

Written by the indexing model from the issue text.