If the nodes are sorted by org-roam we don't want the completion UI to change
the order. In order to disable org-roam sorting set org-roam-node-default-sort
to nil. Then the sorting of the completion UI is used.

Ephemeral buffers are hidden by default in the completion lists,
which is usually desired for background processes.

completion-table-dynamic serves a different purpose. it should only be used if
the candidates are dynamically generated based on the input. This is not the
case for org-roam where we the list of nodes is already available right at the
beginning of the completion. This change should improve performance.