Make Elixir Function optional for LangChain.Function?

[avergin]

For workflows where we just need structured JSON outputs from the models (e.g. data extraction) through using tools, we may not need to execute any code in the client and send any messages back to the models. For such cases, does it make sense to make the function (Elixir Function) attribute optional for LangChain.Function?

(From Anthropic API Docs)

### How tool use works
Integrate external tools with Claude in these steps:

1. Provide Claude with tools and a user prompt
- Define tools with names, descriptions, and input schemas in your API request.
- Include a user prompt that might require these tools, e.g., “What’s the weather in San Francisco?”

2. Claude decides to use a tool
- Claude assesses if any tools can help with the user’s query.
- If yes, Claude constructs a properly formatted tool use request.
- The API response has a stop_reason of tool_use, signaling Claude’s intent.

3. Extract tool input, run code, and return results
- On your end, extract the tool name and input from Claude’s request.
- Execute the actual tool code client-side.
- Continue the conversation with a new user message containing a tool_result content block.

4. Claude uses tool result to formulate a response
- Claude analyzes the tool results to craft its final response to the original user prompt.

**Note: Steps 3 and 4 are optional. For some workflows, Claude’s tool use request (step 2) might be all you need, without sending results back to Claude.**