chore: Bump langsmith in splitter uv (#31626)

`uv lock --upgrade-package langsmith
`
Original issue: The lock file (uv.lock) was constraining
langsmith>=0.1.125,<0.4, preventing LangSmith 0.4.1 installation. Even
though the pyproject.toml wasn't restricting langchain core.


Issue:
https://langchain.slack.com/archives/C050X0VTN56/p1750107176007629

Author: EugeneJinXin