feat: enable streaming for o1 models (#896)

As of a few days ago, o1 models support streaming responses. Please see:
https://community.openai.com/t/openai-o1-streaming-now-available-api-access-for-tiers-1-5/1025430

lua/avante/providers/openai.lua

@@ -147,7 +147,6 @@ M.parse_curl_args = function(provider, code_opts)
   -- NOTE: When using "o1" set the supported parameters only
   local stream = true
   if base.model and string.find(base.model, "o1") then
-    stream = false
     body_opts.max_tokens = nil
     body_opts.temperature = 1
   end