common/chat : fix LFM2/LFM2.5 reasoning round-trip and <think> leak#24234

pwilkin merged 2 commits into

ggml-org:masterggml-org/llama.cpp:masterfrom

tdakhran:tarek/feat/lfm2-thinking-fixtdakhran/llama.cpp:tarek/feat/lfm2-thinking-fixCopy head branch name to clipboard