fix: only allow hex addresses when creating notifications

[Prithpal-Sooriya]

Explanation

we do not support solana or non evm addresses. If we want to support this, then we would need a backend update to prevent a 400 bad requests

References

Changelog

@metamask/notification-services-controller

• FIXED: Added isValidHexAddress when fetching keyring accounts to ensure we only get hex addresses
• FIXED: Added cleanup logic to remote saved notification user storage blobs to only support hex addresses.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes