fix: align lua oop (#889)

lua/cmp_avante/mentions.lua

@@ -1,18 +1,20 @@
 local api = vim.api
 
----@class mentions_source
+---@class mentions_source : cmp.Source
 ---@field mentions {description: string, command: AvanteMentions, details: string, shorthelp?: string, callback?: AvanteMentionCallback}[]
 ---@field bufnr integer
 local mentions_source = {}
+mentions_source.__index = mentions_source
 
 ---@param mentions {description: string, command: AvanteMentions, details: string, shorthelp?: string, callback?: AvanteMentionCallback}[]
 ---@param bufnr integer
-function mentions_source.new(mentions, bufnr)
-  ---@type cmp.Source
-  return setmetatable({
-    mentions = mentions,
-    bufnr = bufnr,
-  }, { __index = mentions_source })
+function mentions_source:new(mentions, bufnr)
+  local instance = setmetatable({}, mentions_source)
+
+  instance.mentions = mentions
+  instance.bufnr = bufnr
+
+  return instance
 end
 
 function mentions_source:is_available() return api.nvim_get_current_buf() == self.bufnr end