timeline: improve handling of edits

- If an edit fails, find Some Way™ to reflect that in the timeline
- revert to the unedited version of the item?
- add a way to re-send the edit?
- If an edit succeeds, mark the item as such, and don't replace it with the previous unedited version (if it comes late from sync), see also https://github.com/element-hq/element-x-ios-rageshakes/issues/2126#issuecomment-2315708428
- but handle that another edit can come from another client through sync :eyes:
- #3948
- https://github.com/matrix-org/matrix-rust-sdk/issues/3941

Start by reading the linked issues #3948 and matrix-rust-sdk #3941, plus the referenced Element X discussion, to understand the intended edit lifecycle. Trace the timeline edit and sync entry points identified there. Done means failed edits are represented or resendable, successful edits remain visible despite late sync data, and edits from other clients are handled.

Written by the indexing model from the issue text.