Add tool support

[mcandru]

The LLM library now supports tool calling: https://simonwillison.net/2025/May/27/llm-tools/

[mcandru]

TODO:

• Implement the LLM chain API
• Switch over to making LLM calls async, as defined in Use Async models where available #2
• Implement stricter input context limits to prevent people from using up all of my credits
• Figure out the interface for using tools