Fix the reviewer filter for snapshot test diffs

An agent added about 40 Jest snapshot tests before a refactor. When they all fail at once, people run jest -u and accept the whole diff unread, so a removed accessibility attribute slips through. Your team wants a filter that lists only the attribute changes a person must read.

An assistant wrote review_snapshot_diff(before, after). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• before: one component's attributes in the old snapshot, as strings like "aria-disabled=true".
• after: the same component's attributes in the new snapshot, in the same format.
• Return the keys a reviewer must read, as a list of strings.

Rules the tests check:

• Split each entry at its first =. The key is the text before it, the value is all the text after it. The value can be empty.
• Skip an entry with no = or with an empty key.
• When a key appears more than once in one list, the last entry wins.
• Cosmetic keys are never reported. They are exactly "class", "style" and any key that starts with "data-".
• Report every other key whose value changed, that is in before but not in after, or that is in after but not in before.
• A key that appears or disappears counts as a change even when its value is empty.
• Keys and values compare exactly. Case and spaces matter.
• Return each reported key once, sorted by plain string order, so uppercase letters come before lowercase ones. Nothing to report returns an empty list.