feature: add resumable picker option

[wvffle]

Did you check the docs?

• I have read all the snacks.nvim docs

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

I'd like to migrate to snacks explorer. One of the things that is bothering me is that after opening and closing (I'm using auto_close), it overrides the last opened picker and Snacks.picker.resume() then opens the explorer.

Describe the solution you'd like

Add an option like resumable = true | false to picker options, so we can filter out pickers that we don't want to override the last opened picker.

Describe alternatives you've considered

none

Additional context

No response