[Breaking] Update Evaluation Functionality (#7388)

- Migrate from deprecated langchainplus_sdk to `langsmith` package
- Update the `run_on_dataset()` API to use an eval config
- Update a number of evaluators, as well as the loading logic
- Update docstrings / reference docs
- Update tracer to share single HTTP session

docs/api_reference/create_api_rst.py

@@ -20,7 +20,9 @@ def load_members() -> dict:
                 cls = re.findall(r"^class ([^_].*)\(", line)
                 members[top_level]["classes"].extend([module + "." + c for c in cls])
                 func = re.findall(r"^def ([^_].*)\(", line)
-                members[top_level]["functions"].extend([module + "." + f for f in func])
+                afunc = re.findall(r"^async def ([^_].*)\(", line)
+                func_strings = [module + "." + f for f in func + afunc]
+                members[top_level]["functions"].extend(func_strings)
     return members