[doc] Replace README recommendation of neodev with lazydev

[Terseus]

In the Neodev README we can see this warning:

Development of neodev.nvim is now EOL. If you're on Neovim >= 0.10, then I highly suggest you to use lazydev.nvim It's a much faster and better replacement for neodev.

However Neotest README still recommends to use Neodev:

It is highly recommended to use neodev.nvim to enable type checking for neotest to get type checking, documentation and autocompletion for all API functions.

It would be great if we not only change the recommendation but also adapt the Neodev recommended config snippet to Lazydev.