Persist the "filter options" over the session lifecycle

hey nvim-tree builders,

I would like to raise a small feature request to you, which may increase the nvim-tree UX a bit, just for your reference. Thanks a lot for building this useful tool.

Is this a question?
No

Can this functionality be implemented utilising API?
I'm not very sure about this, but with a preliminary search in the API, I didn't find a very straight-forward way to implement it.

Is your feature request related to a problem? Please describe.

I set the nvim-tree to update root dir following the buffer switch, I often switch back and forth between two git projects which have different root ofc. The default setting recognizes .gitignore, so, in a project, if I need to inspect some git ignored files, I have to turn off the ignore filter by I key, navigate to the ignored directory and open the target file. But quickly, I ran into two problems:

• When I switch to another file in a different root dir, then switch back later, I expected the tree view is exactly the same as I left it, i.e. a view showing all ignore dirs/files are still there and focus follows my opened file, it means my previous filter toggle is still functioning. However, they are all gone, i have to toggle ignore filter again to show those ignored files.
• After I toggle ignore filter again, the tree-view didn't refresh to follow the opened file automatically, I have to navigate to the deep dir which contains that file...

      update_focused_file = {
        enable = true,
        update_root = {
          enable = true,
          ignore_list = {},
        },
        exclude = false,
      },

Describe the solution you'd like

• The filter options can persist across root dir switchs, and be a session level setting.
• Once set, it can apply on all the root dirs you switch to.
• The tree focus can follow the files on the ignore list, only if you turn off the ignore filter for current session.
• The setting doesn't change the default settings, in a new vim session, all the filter option changes are gone.

Start by tracing the I key filter toggle and the update_focused_file.update_root lifecycle described in the issue. Check how filter state and focus are handled when switching roots, then verify that the state persists only within a session and that focus follows ignored files when the filter is disabled.