fix(build): distinguish vim.mpack from global require'mpack'

problem: the api of vim.mpack is not compatible with a system provided mpack
solution: don't require 'mpack' directly from the system path

src/nvim/generators/gen_api_dispatch.lua

@@ -1,4 +1,4 @@
-local mpack = require('mpack')
+local mpack = vim.mpack
 
 local hashy = require'generators.hashy'