refactor(config): change way how it handles options

lua/gopher/config.lua

@@ -1,18 +1,10 @@
----@class Config
----@field commands ConfigCommands
+---@class gopher.Config
+local config = {}
 
----@class ConfigCommands
----@field go string
----@field gomodifytags string
----@field gotests string
----@field impl string
----@field iferr string
----@field dlv string
-
-local M = {
-  ---@type Config
-  config = {
-    ---set custom commands for tools
+---@class gopher.Config
+---@field commands gopher.ConfigCommands
+local default_config = {
+  ---@class gopher.ConfigCommands
   commands = {
     go = "go",
     gomodifytags = "gomodifytags",
@@ -21,13 +13,15 @@ local M = {
     iferr = "iferr",
     dlv = "dlv",
   },
-  },
 }
 
----Plugin setup function
----@param opts Config user config
-function M.setup(opts)
-  M.config = vim.tbl_deep_extend("force", M.config, opts or {})
+---@param user_config gopher.Config|nil
+function config.setup(user_config)
+  config = vim.tbl_deep_extend("force", {}, default_config, user_config or {})
 end
 
-return M
+-- setup ifself, needs for ability to get
+-- default config without calling .setup()
+config.setup()
+
+return config