Resolve the LangSmith project name if tracing is configured.
Checks for the required API key and tracing environment variables.
When both are present, resolves the project name with priority:
settings.deepagents_langchain_project (from
DEEPAGENTS_LANGSMITH_PROJECT), then LANGSMITH_PROJECT from the
environment (note: this may already have been overridden at import
time to match DEEPAGENTS_LANGSMITH_PROJECT), then 'default'.
get_langsmith_project_name() -> str | None