langchain-core 1.6.1

Changes since langchain-core==1.6.0

revert: release(core): 1.6.2 (#39971) release(core): 1.6.2 (#39967) fix(core): shore up indexing in genai v1 streaming content (#39964) fix(core): make StructuredTool JSON-serializable (#39631) chore(deps): bump minor and patch dependencies (#39869) release(core): 1.6.1 (#39832) feat(core): propagate gateway information on error path (#39829)