chore: correctly handle empty vault patches

I think `unwrap_or_default()` turns a remove into a zero word. I don't think we eventually want this, even if for now it will work correctly because the protocol does not generate `Remove`. Let's make it an `expect()` for now and add an issue to address this later

_Originally posted by @igamigo in https://github.com/0xMiden/rust-sdk/pull/2290#discussion_r3583722378_

Find the code handling vault patches, likely in a file related to transactions or state updates. Look for `unwrap_or_default()` on a patch operation. Change it to an `expect()` with a descriptive message. Run existing tests to ensure the change doesn't break current functionality, as the protocol currently doesn't generate `Remove` operations.

Scritto dal modello di indicizzazione a partire dal testo della issue.