FIX: adjust token limits to account for functions (#96)

Reduce maximum replies to 2500 tokens and make them even for both GPT-3.5
and 4

Account for 400+ tokens in function definitions (this was unaccounted for)

lib/modules/ai_bot/open_ai_bot.rb

@@ -15,22 +15,21 @@ module DiscourseAi
       def prompt_limit
         # note GPT counts both reply and request tokens in limits...
         # also allow for an extra 500 or so spare tokens
+        #
+        # 2500 are the max reply tokens
+        # Then we have 400 or so for the full function suite
+        # 100 additional for growth around function calls
         if bot_user.id == DiscourseAi::AiBot::EntryPoint::GPT4_ID
-          8192 - 3500
+          8192 - 3000
         else
-          16_384 - 2000
+          16_384 - 3000
         end
       end
 
       def reply_params
-        max_tokens =
-          if bot_user.id == DiscourseAi::AiBot::EntryPoint::GPT4_ID
-            3000
-          else
-            1500
-          end
-
-        { temperature: 0.4, top_p: 0.9, max_tokens: max_tokens }
+        # technically we could allow GPT-3.5 16k more tokens
+        # but lets just keep it here for now
+        { temperature: 0.4, top_p: 0.9, max_tokens: 2500 }
       end
 
       def submit_prompt(

spec/lib/modules/ai_bot/jobs/regular/create_ai_reply_spec.rb

@@ -36,7 +36,7 @@ RSpec.describe Jobs::CreateAiReply do
           req_opts: {
             temperature: 0.4,
             top_p: 0.9,
-            max_tokens: 1500,
+            max_tokens: 2500,
             functions: bot.available_functions,
             stream: true,
           },