The last remaining threaded operation in dynamic ratsnest was the
recalculation of the dynamic connectivity map. Because we do not
require any of the extra features of the connectivity map, we can get
away with a lightweight move of the anchors to update the ratsnest. The
resulting connectivity tree is not valid but it is not needed for the
ratsnest, which only needs a list of nets/anchors.
List of hidden nets stored in project local settings
Hide/Show actions in context menu only for now, will
add them to some more GUI places soon.
Ref https://gitlab.com/kicad/code/kicad/-/issues/1951
avoid potential performance issues when the dialog is still listening to
the board updates and refreshing its data and view structures.
it seems useful to keep the settings of the dialog across dialog
open-close cycles.