Pip install of langchain fails in python3.13t (nogil/free threading) due to orjson

### Checked other resources - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [x] langchain-core - [ ] langchain-cli - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-perplexity - [ ] langchain-prompty - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Example Code (Python) ```python import langchain # will not exist, because installation failed ``` ### Error Message and Stack Trace (if applicable) ```shell Compiling orjson v3.11.5 (/tmp/pip-install-gzfpt7nq/orjson_810ee428eae44b9fa95b90d5d0df5439) error: failed to run custom build command for `orjson v3.11.5 (/tmp/pip-install-gzfpt7nq/orjson_810ee428eae44b9fa95b90d5d0df5439)` Caused by: process didn't exit successfully: `/tmp/pip-install-gzfpt7nq/orjson_810ee428eae44b9fa95b90d5d0df5439/target/release/build/orjson-709b84c04d20a8fb/build-script-build` (exit status: 1) --- stderr orjson v3.11.5 does not support free-threaded Python warning: build failed, waiting for other jobs to finish... 💥 maturin failed Caused by: Failed to build a native library through cargo …