refactor: correctness fixes, API modernization, and cleanup

lua/dap/hover/node.lua

@@ -93,6 +93,7 @@ function Node:index_of(target)
     return search(self)
 end
 
+---@async
 ---@param session dap.Session
 function Node:expand_all(session)
     if not self:is_expandable() then
@@ -139,6 +140,7 @@ end
 function Node:is_c_pointer()
     return self:is_c_lang()
         and self:is_container()
+        and self.item.type ~= nil
         and self.item.type:match(
                 "%*%s*[const%s]*[volatile%s]*[restrict%s]*$"
             )