Expose timeout to search function

[captain828]

Right now, a fixed timeout is used in the internal _search function of 100 seconds.

tavily.py:37 - response = requests.post(self.base_url, data=json.dumps(data), headers=self.headers, timeout=100)

I want to suggest the following improvements:

• expose the timeout as a function arg, much like how the OpenAI SDK does it
• set a more reasonable default timeout, like 30 seconds

Let me know what you think.