feat: diff navigation

[azorng]

add navigation to diff module + general improvements

 diff = {
        open = '<leader>gd',                 -- Opens a diff view tab of a selected file modified by goose since the last prompt
        next = '<leader>g]',                 -- Navigate to next file diff
        prev = '<leader>g[',                 -- Navigate to previous file diff
        close = '<leader>gc',                -- Close diff view tab and return to normal editing
 }