tomlkit: appending to a split [[array]] is silently lost

In tomlkit 0.15.1+ (master as of 2026-10-29), if an array of tables is split by another table ([[x.a]] ... [y] ... [[x.a]]), then doc['x']['a'].append({...}), insert, del and item assignment do nothing: no error, and unwrap()/dumps() are unchanged. doc['x'] is an OutOfOrderTableProxy, and its AoT is a freshly merged list built from the fragments, so mutations hit only that throwaway list. In-place edits of existing elements do work. Workaround: re-read with tomllib after editing, or get the AoT from the container part that holds the last fragment. A fix routes mutations to the owning fragment (and removes a fragment once emptied, or it renders as a = []).