docs: move `standard-tests` or add dedicated section in API ref

[mdrxy]

URL

https://python.langchain.com/api_reference/standard_tests/index.html

Checklist

• I added a very descriptive title to this issue.
• I included a link to the documentation page I am referring to (if applicable).

Issue with current documentation:

Package is buried in the list of partner integrations

Idea or request for content:

Put under dedicated sub-header or put at top of list