Consider revisiting `NoteFile` variants

> Not related to this PR, but I do wonder whether it was a good idea to include `NoteId` as a variant in this enum. Seems like it is somewhat misleading that `NoteFile` contains just the note ID.

_Originally posted by @bobbinth in https://github.com/0xMiden/miden-base/pull/1976#discussion_r2413015698_

The `NoteFile` enum was added mainly to support the concept of note importing/exporting. Specifically, the idea of the `NoteId` variant was to be a way of communicating public note IDs that could be retrieved from the node.