Clean obsolete BABE's weight data (#10748)

* Clean obsolete BABE weight data
* Take out test assertion from check closure
* Optimize metadata access using `HeaderMetadata` trait
* Apply suggestions from code review
* Introduce finalize and import pre-commit synchronous actions
* Do not hold locks between internal methods calls
* Remove unused generic bound
* Apply suggestions from code review
* Register BABE's pre-commit actions on `block_import` instead of `start_babe`
* PreCommit actions should be `Fn` instead of `FnMut`
* More robust safenet in case of malformed finality notifications

Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: André Silva <[email protected]>