Expose fine-grained update method

The `Update` request is now also implemented resource paths other than the root model, so we can expose an `.update()` method on all object types (27R1+).

Start by locating the Update request implementation and the object types that currently expose updates only through the root model. Trace how resource paths are handled for the 27R1+ API, then add the .update() entry point consistently across object types and verify that each targets its own resource path.

Written by the indexing model from the issue text.