Live Data cells leak an edit bus listener each time they are displayed

Each Live Data cell registers a listener on the edit bus when it is mounted (BaseDisplayer.vue, logic.getEditBus().onAnyEvent(...)) and never removes it. EditBusService has no way to unregister a listener.

Consequences

• Every page change, sort or filter that displays new rows adds one permanent listener per displayed cell. With 15 rows and 6 columns, 10 page changes leave about 900 listeners.
• The listeners keep the unmounted cell components reachable, so they are never garbage collected.
• Every edit event (start, cancel, save) calls all the listeners ever registered, so inline editing gets slower the longer the user browses the Live Data.

Steps to reproduce

1. Open a page with a Live Data, for instance the document index.
2. Navigate between pages of the Live Data several times.
3. Take a heap snapshot: the detached BaseDisplayer instances stay alive, held by the edit bus listeners.

Expected: a cell removes its listener when it is unmounted.