This PR adds the initial groundwork for invoking tools in response to
tool uses from the model.
Tool uses are run when the model responds with a `stop_reason` of
`tool_use`.
Currently the tool results are just inserted as text into the user
message. We'll want to include these as `tool_result` content on the
message, but Claude seems to understand it regardless.
Release Notes:
- N/A
This PR adds a tool registry to hold tools that can be called by the
Assistant.
Currently we just have a `now` tool for retrieving the current datetime.
This is all behind the `assistant-tool-use` feature flag which currently
needs to be explicitly opted-in to in order for the LLM to see the
tools.
Release Notes:
- N/A