Upgrade @metamask/token-search-discovery-controller to version 4.0.0

A new major version of `@metamask/token-search-discovery-controller`, 4.0.0, 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.

Locate the project references to @metamask/token-search-discovery-controller and inspect how the current version is declared. Update the dependency to 4.0.0, then run the repository's existing validation checks to confirm the extension still builds and tests pass.

Written by the indexing model from the issue text.