feat: support .py, .R, .jl files in QuartoPreview (#203)

* Initial plan

* feat: support .py, .R, .jl files in QuartoPreview

Agent-Logs-Url: https://github.com/quarto-dev/quarto-nvim/sessions/108ce2fc-b504-46ab-aa70-47f193830d99

Co-authored-by: jmbuhr <17450586+jmbuhr@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jmbuhr <17450586+jmbuhr@users.noreply.github.com>

Author: Copilot

lua/quarto/init.lua

@@ -59,7 +59,7 @@ function M.quartoPreview(opts)
   end
 
   -- Check file extensions
-  local quarto_extensions = { '.qmd', '.Rmd', '.ipynb', '.md' }
+  local quarto_extensions = { '.qmd', '.Rmd', '.ipynb', '.md', '.py', '.R', '.jl' }
   local file_extension = buffer_path:match '^.+(%..+)$'
   if mode == 'file' and not file_extension then
     vim.notify 'Not in a file. exiting.'