refactor: replace custom util with api fn

I was using a function that turns list-like tables
into sets to quickly search the filetype_exclude
table. This commit replaces that tool with one
from vim.api and adds error handling to ensure
that filetype_exclude is a list-like table.

lua/tidy/init.lua

@@ -12,21 +12,9 @@ function M.toggle()
   end
 end
 
-local function list_to_set(list)
-  local set = {}
-
-  for _, item in ipairs(list) do
-    set[item] = true
-  end
-
-  return set
-end
-
 local function is_excluded_ft(opts)
   local ft = vim.api.nvim_buf_get_option(0, "filetype")
-  local ft_set = list_to_set(opts.filetype_exclude)
-
-  return ft_set[ft]
+  return vim.list_contains(opts.filetype_exclude, ft)
 end
 
 local function reset_cursor_pos(pos)
@@ -55,6 +43,14 @@ function M.setup(opts)
 
   opts = vim.tbl_extend("force", defaults, opts or {})
 
+	if not vim.tbl_islist(opts.filetype_exclude) then
+		vim.notify(
+			"tidy.nvim: filetype_exclude option must be a list-like table...",
+			vim.log.levels.ERROR,
+			{ title = "Tidy" }
+		)
+	end
+
   local tidy_grp = vim.api.nvim_create_augroup("tidy", { clear = true })
 
 	vim.api.nvim_create_autocmd("BufWritePre", {