fix: add function close_existing_buffer_by_name back

lua/chatgpt_nvim/init.lua

@@ -54,6 +54,16 @@ local function read_file(path)
   return data
 end
 
+-- Added function to close existing buffers matching a name pattern.
+local function close_existing_buffer_by_name(name_pattern)
+  for _, buf in ipairs(vim.api.nvim_list_bufs()) do
+    local buf_name = vim.api.nvim_buf_get_name(buf)
+    if buf_name:match(name_pattern) then
+      vim.api.nvim_buf_delete(buf, {force = true})
+    end
+  end
+end
+
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 -- PROMPT CONSTRUCTION
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