fix: correctly set disable_parallel_tool_use

[dannykopping]

Relates to #2.

Currently we're indiscriminately setting disable_parallel_tool_use in the any type: this is a correctness bug.
We should only set this field for the type which is set.

https://platform.claude.com/docs/en/agents-and-tools/tool-use/implement-tool-use#parallel-tool-use

There are 4 types: auto, any, tool, none. none is irrelevant (can't parallelize tool calls which don't occur).

We should check which type is used (or set auto if none is provided) and set the field on that.

---

I noticed this today when using Claude Code v2.0.69.

The request did not contain a tool_choice field (behavioural change), so I got this error:

{
    "error": {
        "message": "Thinking may not be enabled when tool_choice forces tool use.",
        "type": "invalid_request_error"
    },
    "request_id": "",
    "type": "error"
}

[ssncferreira]

LGTM, just a small nit 👍