needs_layout update does not lead to clean build

[ubmarco]

I observed that a change in needs_layouts does not lead to a clean build. That's unexpected as relevant output pages do not get updated.

This is how it's defined:

    layouts: dict[str, dict[str, Any]] = field(
        default_factory=dict, metadata={"rebuild": "html", "types": ()}
    )

I think the rebuild key should be set to env. Other configuration parameters should also be cross-checked for an impact on the incremental build.