Address open questions from `SyncTransactions` changes

#2304 added a field to `SyncTransactions`, mapping each consumed public note's nullifier to its note ID so followers of a public account can later recover the details through `GetNotesById`.

A few questions came up during review that we should address:

- Instead of resolving nullifiers to note IDs with a separate sync-time query, we could store something like `consumed_by_tx_id` directly on the notes table to simplify the flow
- We should rename the message. The current one describes how it is used, not really what it represents. Names like `NoteReference` or `NoteBinding` may fit better
- Once the message is renamed, `SyncTransactionsResponse.consumed_note_refs` could likely become just `consumed_notes`.

Overall we should also revisit if this was the best way to solve https://github.com/0xMiden/node/issues/2296