Backing fixes (#1897)

* Commit my changes

* some backing fixes

* indentation

* fix backing tests

* tweak includability rules

* comment

* Update node/core/backing/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/core/backing/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/core/backing/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update node/core/backing/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
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