Make it clearer that `DirectThingClient` actions don't require dependencies

[rwb27]

When a DirectThingClient is created (e.g. via a FastAPI dependency) any dependencies of its actions are added to the constructor. This means they don't need to be passed manually when the actions are called. However, because the actions accept **kwargs and simply pass that on to the underlying Thing object, if you do supply the dependencies there's no error.

It would be helpful to:

• Check the docs make it clear dependencies need not be supplied
• Check the kwargs don't contain dependencies
• Consider improving client generation so the actions have the correct signature

The last point may take longer.

The reason **kwargs isn't checked carefully is that any unused **kwargs should get picked up by the function call to the underlying action. This won't happen for dependencies though, as dependencies in the incoming arguments will simply be overwritten when they are injected by the method on the DirectThingClient object.

[rwb27]

This will be closed when we get rid of dependencies.