Remove explicit beacon endpoint and enhance eth/head endpoint instead.

[luka-ethernal]

• Create a task that periodically checks for changes in head and updates one global state value.
• Make eth/head endpoint just read the current state instead of calling Node every time.
• Integrate a beacon mapping into eth/head endpoint, so mapping becomes easier and atomic.
• Implement a retry mechanism in case of errors.
• If all retries fail, crash the entire process.
• Introduce versioning to endpoints.

[luka-ethernal]

@QEDK I've addressed all of the comments, please review them if you can.