langchain-openai 1.5.2

Changes since langchain-openai==1.5.1

release(openai): 1.5.2 (#39719) fix(openai): preserve reasoning item boundaries (#39278) release(openai): 1.5.2a1 (#39709) feat(openai): extract gateway metadata from response headers when available (#39706) chore(openai): update snapshots (#39657) fix(openai): support o-series models in get_num_tokens_from_messages (#38710)