Function parse_streaming_thinking 

pub fn parse_streaming_thinking(
    text: &str,
    is_thinking: bool,
    buffer: &mut String,
) -> (String, Option<String>, bool)

Parse thinking tags from streaming content.

Handles <think>...</think> and <thought>...</thought> tags that may be split across multiple chunks. Returns (actual_text, reasoning_delta, new_is_thinking).