Cleanup of the `state-machine` crate (#3524)

* Start refactoring state-machine crate

* More improvement to state-machine

* Fix tests compilation on master and remove warnings

* Fix compilation

* Apply suggestions from code review

Co-Authored-By: Sergei Pepyakin <[email protected]>

* Update core/state-machine/src/basic.rs

Co-Authored-By: DemiMarie-parity <[email protected]>

* Line width

* Update core/primitives/src/storage.rs

Co-Authored-By: Benjamin Kampmann <[email protected]>

* Update core/state-machine/src/error.rs

Co-Authored-By: Benjamin Kampmann <[email protected]>

* Review feedback