refactor: replace vim.loop with vim.uv

[mrr11k]

This PR uses vim.uv instead of the deprecated vim.loop.

See neovim/neovim#22846 for more info.

[purarue]

The lazy instructions use a or, incase the user is on older systems to allow using vim.loop still:

if not (vim.uv or vim.loop).fs_stat(lazypath) then

I know kickstart targets stable, but should probably match that instead of requiring the user to be on v0.10+, would lead to one less error if a user happened to be on an old version

[feoh]

I think this is obviated by #936 please feel free to re-open if I'm wrong.