Add multi-format tool call parser (bracket, raw JSON)

[janhilgard]

Summary

Add support for multiple tool calling formats that models output:

• Qwen3 bracket: [Calling tool: function_name({"arg": "value"})]
• Raw JSON (fallback): {"name": "...", "arguments": {...}} - single or multiple

Changes

• New regex parser for Qwen3 bracket format (highest priority)
• New _parse_raw_json_tool_calls() helper for raw JSON parsing (lowest priority fallback)
• Handles JSON arrays and multiple JSON objects with balanced brace detection
• Properly extracts function name and JSON arguments
• Cleans parsed content from response text

Why Raw JSON Fallback?

Some models (including Qwen3) may output plain JSON tool calls without wrapper tags. The raw JSON parser activates only when no other format matches, preventing false positives.

Testing

Tested with Qwen3-30B-A3B-Instruct-2507-MLX-6bit model:

curl -X POST http://localhost:1239/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "...",
    "messages": [{"role": "user", "content": "Search for SaaS pricing"}],
    "tools": [{"type": "function", "function": {"name": "searchReddit", "parameters": {...}}}]
  }' | jq '.choices[0].message'

# Result:
{
  "role": "assistant",
  "content": null,
  "tool_calls": [{"id": "call_...", "type": "function", "function": {"name": "searchReddit", "arguments": "{...}"}}]
}

🤖 Generated with Claude Code

[waybarrios]

Thanks for the contribution! Added a small fix for black formatting.