feat(minor): extract reasoning from LLM response if within thought-delimiters
Some LLM APIs include the reasoning part within delimiters like `<think> ... </think>`, rather than in a separate `reasoning` field.
The delimiters are configurable via `LLMConfig.reasoning_delimiters: Tuple[str,str]`.
This feature extracts such reasoning and puts it in the `reasoning` field of the Langroid `LLMResponse` object.
See example `examples/reasoning/agent-reasoning.py` and try with `ollama/deepseek-r1:32b` (the full R1 API does
give a separate `reasoning_content` field in the API result, but the distills do not).