refactor: message content (#1424)

lua/avante/utils/tokens.lua

@@ -9,6 +9,21 @@ local cost_per_token = {
   davinci = 0.000002,
 }
 
+---@param content AvanteLLMMessageContent
+---@return integer
+function Tokens.calculate_message_content_tokens(content)
+  if type(content) == "string" then return Tokens.calculate_tokens(content) end
+  local tokens = 0
+  for _, item in ipairs(content) do
+    if type(item) == "string" then
+      tokens = tokens + Tokens.calculate_tokens(item)
+    elseif item.type == "text" then
+      tokens = tokens + Tokens.calculate_tokens(item.text)
+    end
+  end
+  return tokens
+end
+
 --- Calculate the number of tokens in a given text.
 ---@param text string The text to calculate the number of tokens for.
 ---@return integer The number of tokens in the given text.