previewers.file_maker freezes neovim when/while file read is slow

[FelipeLema]

Description

let's say I have a slow-access mount at /home/myuser/slow-access-mnt. If I call :Telescope find_files and move the selection towards one of those files, neovim freezes until preview is ready or it times out.

the freezing comes from previewers.file_maker waiting on capture("file --mime-type -b …"), since it blocks waiting for that command's output. Replacing that call with an async call (probably using vim.uv) should avoid neovim freezing.

on the same matter, a "preview loading" message would be welcome as an UX plus

Neovim version

NVIM v0.10.2
Build type: Release
LuaJIT 2.1.1713484068
Run "nvim -V1 -v" for more info

Operating system and version

debian 12

Telescope version / branch / rev

a0bbec2

checkhealth telescope

==============================================================================
telescope: require("telescope.health").check()

Checking for required plugins ~
- OK plenary installed.
- OK nvim-treesitter installed.

Checking external dependencies ~
- OK rg: found ripgrep 13.0.0
- OK fd: found fdfind 8.6.0

===== Installed extensions ===== ~

Telescope Extension: `frecency` ~
- OK nvim-web-devicons installed.
- OK ripgrep installed.

Telescope Extension: `fzf` ~
- OK lib working as expected
- OK file_sorter correctly configured
- OK generic_sorter correctly configured

Steps to reproduce

1. have a mount that have slow read (you can try using mkfifo /some/path to simulate a file with slow read)
2. :Telescope find_files
3. do stuff while preview is loading for that mount

Expected behavior

neovim is responsive while preview is loading

maybe show a "preview is loading" message

Actual behavior

check that stuff inputted in last step is not inputted right away, but rather queued until previewer is done

Minimal config

-- any recent Telescope version

[FelipeLema]

willing to do a PR to fix it if maintainers are willing to accept

[FelipeLema]

also willing to tidy up the whole filetype-mime-filesize-timeout-hook code if maintainers are willing to accept