Startuptime optimization: don't eager load module in `plugin/`

[tuurep]

See :h lua-plugin-lazy

• Keep plugin/<name>.lua small, avoid eagerly calling require() on modules
  until a command or mapping is actually used.

So I think what would be ideal for startuptime would be this:

• The entry point that does the require(...) is the usercommand RegisterEditor
  • So basically the only role of plugin/registereditor.lua is to create the usercommand
• After Update open register windows when register contents are modified #12, also setup the autocmds only after the first require(...)

Question: I've always wondered what the effect of requiring the same lua module on every use of the command is, but based on everything I've read, that's how it should be done?