improve `buffers-panel` UX

[mmahmoudian]

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

I personally find the buffers-panel very useful, and I somewhat see it as Emacs' ibuffer alternative. But there are few usability perks that can be improved, as at the current state it can only be used to list the buffers and use mouse to switch to them.

Describe the solution you'd like

I propose the following features which are somewhat based on the treemacs and ibuffer:

1. a way to put focus on the panel. At the moment there is no way to use keyboard to put focus on the panel
2. use C-n / C-p or arrow keys to navigate through the panel
3. use d to mark buffer for bulk deletion
4. use D for deleting the buffer at point. Also middle mouse click to kill that buffer.
5. the width of the panel can be configured for example by dragging the border with mouse.

Describe alternatives you've considered

I cannot think of alternatives for 1, 2, and 4, but for 3 the user can use C-Space to mark.

Additional context

I use Nyxt as a keyboard-focused browser that somewhat can behave similar to Emacs. I accidentally found the buffers-panel and I like it for what it is, but at the moment the only part that works with keyboard is spawning the panel.

[jmercouris]

All of these things depend on a proper window management system. These are very good points. They will be addressed hopefully sometime in the Nyxt 4.X series.