Switch to nvim-nio for async

[cseickel]

https://github.com/nvim-neotest/nvim-nio

This was mentioned a few times by @pysan3 and I'd like to make a separate issue for it. I took a look at nio and I do really like it. Things that will be helpful for us:

1. It supports cancellation (this is huge)
2. It has built-in methods for lsp and some libuv fs actions (It might be a good idea to see about adding directory scanning into nio itself if we use it)
3. Maybe it can be used to fix the hell that is testing asynchronous actions in neo-tree.
4. It is a really nice and simple api.

If they had support for running jobs like plenary, and if we switch to pathlib, then I don't think we need plenary at all anymore as a runtime requirement. Not that it really matters as everyone has plenary installed anyhow.

[pysan3]

I've got that already in pathlib.nvim: https://github.com/pysan3/pathlib.nvim?tab=readme-ov-file#scan-directories
and it supports depth and follow_symlinks: https://pysan3.github.io/pathlib.nvim/doc/PathlibPath.html#PathlibPath.fs_iterdir
Example: https://github.com/pysan3/pathlib.nvim/blob/main/spec/measure_time_with_linux_source_code.lua
(Run it with nvim --headless -c ':so ./spec/measure_time_with_linux_source_code.lua' -c ':noa qa!' and tail -f measure.log)

For tests, you might want to look into this: https://github.com/lewis6991/nvim-test
I haven't used it yet but I saw it being recommended in some places.

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plenary.job-like feature is being worked on right now: nvim-neotest/nvim-nio#5

[pysan3]

Quick update. nio.process is now merged and released as v1.5.0.