configuration: minor improvements / fixes

Could not extend the subclass of 'TypedDict' the way I wanted, so I switched to 'dataclass'.

chatmastermind/api_client.py

@@ -30,17 +30,15 @@ def ai(chat: ChatType,
     Make AI request with the given chat history and configuration.
     Return AI response and tokens used.
     """
-    if not isinstance(config['openai'], dict):
-        raise RuntimeError('Configuration openai is not a dict.')
     response = openai.ChatCompletion.create(
-        model=config['openai']['model'],
+        model=config.openai.model,
         messages=chat,
-        temperature=config['openai']['temperature'],
-        max_tokens=config['openai']['max_tokens'],
-        top_p=config['openai']['top_p'],
+        temperature=config.openai.temperature,
+        max_tokens=config.openai.max_tokens,
+        top_p=config.openai.top_p,
         n=number,
-        frequency_penalty=config['openai']['frequency_penalty'],
-        presence_penalty=config['openai']['presence_penalty'])
+        frequency_penalty=config.openai.frequency_penalty,
+        presence_penalty=config.openai.presence_penalty)
     result = []
     for choice in response['choices']:  # type: ignore
         result.append(choice['message']['content'].strip())