docs: Align crate-level documentation with ext_ features

I think the crate-level documentation is now missing some ext_ features. We might add them to the list when we consolidate features for the next release.

Inspect the crate-level documentation and compare its feature list with the available ext_ features. Confirm which ext_ features are missing and update the documentation during the planned feature consolidation; done means the documented list matches the intended features for the next release.

Written by the indexing model from the issue text.