Upgrade @metamask/multichain-transactions-controller to version 7.0.0

A new major version of `@metamask/multichain-transactions-controller`, 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.

Start by checking whether @metamask/multichain-transactions-controller is present in this project and identify where its version is declared. Upgrade it to 7.0.0, then verify that the project still builds and its existing checks pass. The issue is stale and does not name a file or test, so confirm the package location before starting.

Written by the indexing model from the issue text.