refactor: correctness fixes, API modernization, and cleanup

lua/dap/hover.lua

@@ -11,9 +11,7 @@ local function hover_async()
         return
     end
 
-    local win = Window.get_instance(session)
-    if win.winid and vim.api.nvim_win_is_valid(win.winid) then
-        vim.api.nvim_set_current_win(win.winid)
+    if Window.focus_if_shown() then
         return
     end
 
@@ -115,7 +113,7 @@ local function hover_async()
     local item = Item.new(expr, resp.type, resp.result, resp.variablesReference)
     local root = Node.new(item, nil, session.filetype)
     root:load_children(session)
-    win:show(root)
+    Window.show(session, root)
 end
 
 local function hover()