Making it possible to use buftype=nofile for Chat

[itsfrank]

Loving this plugin, but using it with set hidden is rather frustrating.

I use a keymap to toggle the chat window on/off. While I'm working in neovim, this is fantastic. However anytime I try to close neovim, I get the error No write since last change which forces me to force quit with :q!.

I often close neovim with the :wqa command and that will also fail because the chat plugin is perpetually in a modified state (by design i think).

The closing behavior is a trivial fix if I can make the chat buffer nofile. E.g. with a keymap like so:

vim.keymap.set("n", "<leader>gpt", function()
    codecompanion.toggle()

    local current_buffer = vim.api.nvim_get_current_buf()
    local buffer_name = vim.api.nvim_buf_get_name(current_buffer)
    if string.find(buffer_name, "%[CodeCompanion%]") then
        vim.api.nvim_buf_set_option(0, "buftype", "nofile")
    end
end)

This works great for not getting the error upon quitting, but it completely breaks chat, because chat relies on sending :w to the buffer in order to send to the LLM. See the implementation of keymaps like <cr> or <C-s> found here.

I believe this is trivially fixable since the callback has a chat object as a parameter, and the implementation of the autocmd for BufWriteCmd is simply chat:submit() found here

By decoupling submission from BufWriteCmd we can let users have more control over the behavior of the buffer, and better support set hidden.

I implemented the trivial fix locally and it seems to work (see draft PR linked below).

An interesting follow-up would be supporting nofile as a first class feature in settings.

[itsfrank]

PR implementing suggested change: #148