Quick fix as follow up to https://github.com/neovim/neovim/pull/26108

kqueue only reports events on a watched folder itself, not for files
created or deleted within. So the approach the PR took doesn't work on FreeBSD.

We'll either need to bring back polling for it, combine watching with manual
file tracking, or disable LSP file watching on FreeBSD

Should help with https://github.com/neovim/neovim/issues/23291

On linux `new_fs_event` doesn't support recursive watching, but we can
still use it to watch folders.

The downside of this approach is that we may end up sending some false
`Deleted` events. For example, if you save a file named `foo` there will
be a intermediate `foo~` due to the save mechanism of neovim.

The events we get from vim.uv in that case are:

- rename: foo~
- rename: foo~
- rename: foo
- rename: foo
- change: foo
- change: foo

The mechanism in this PR uses a debounce to reduce this to:

- deleted: foo~
- changed: foo

`foo~` will be the false positive.
I suspect that for the LSP case this is good enough. If not, we may need
to follow up on this and keep a table in memory that tracks available
files.

The watch_file test started failing on bsd after
3ca967387c49c754561c3b11a574797504d40f38.

test(fs): vim.loop has been replaced with vim.uv

Problem:
helpers.tmpname() may create a local file, depending on circumstances.

Solution:
Only use helpers.tmpname() for its parent directory (the "temp root").
Use fs_mkdtemp() to actually get a unique name.

Co-authored-by: Lewis Russell <lewis6991@gmail.com>

test: replace lfs with luv

luv already pretty much does everything lfs does, so this duplication
of dependencies isn't needed.