bug: custom latex template in markdown

[yuukibarns]

Did you check docs and existing issues?

• [x] I have read all the snacks.nvim docs
• [x] I have updated the plugin to the latest version before submitting this issue
• [x] I have searched the existing issues of snacks.nvim
• [x] I have searched the existing issues of plugins related to this issue

Neovim version (nvim -v)

10.4

Operating system/version

archlinux

Describe the bug

reopen https://github.com/folke/snacks.nvim/issues/1262

Steps To Reproduce

no

Expected Behavior

In 2ee64887c2be80c6b7b8fac4bb0617c827fde0d0, packages in the preamble of tex are included but I hope to use more packages in markdown where no preamble is available, so I hope to have an option for custom latex preamble in markdown.

Repro

vim.env.LAZY_STDPATH = ".repro"
load(vim.fn.system("curl -s https://raw.githubusercontent.com/folke/lazy.nvim/main/bootstrap.lua"))()

require("lazy.minit").repro({
  spec = {
    { "folke/snacks.nvim", opts = {} },
    -- add any other plugins here
  },
})