chore(deps): drop direct langsmith dependency

LangSmith remains available transitively via langchain-core; remove the
redundant top-level pin from pyproject.toml.

Author: Brescou

pyproject.toml

@@ -14,7 +14,6 @@ dependencies = [
     "langchain-community>=0.3,<1.0",
     "langchain-core>=1.3.3,<2.0",
     "langchain-classic>=1.0.7,<2.0",
-    "langsmith>=0.8.0,<1.0",
     "urllib3>=2.7.0",
     "httpx>=0.27",
     "tenacity>=9.0",