[Enhancement] Convert fast-unstake to use StakingInterface, decouplin… (#12424)

* [Enhancement] Convert fast-unstake to use StakingInterface, decoupling it from Staking

* Update primitives/staking/src/lib.rs

Co-authored-by: Kian Paimani <[email protected]>

* Update primitives/staking/src/lib.rs

Co-authored-by: Kian Paimani <[email protected]>

* fix validator comment

* remove todo

* ideas from Kian (#12474)

Co-authored-by: kianenigma <[email protected]>

* Rename StakingInterface -> Staking for nomination-pools

* Staking fixes

* StakingInterface changes

* fix fast-unstake

* fix nomination-pools

* Fix fast-unstake tests

* Fix benches for fast-unstake

* fix is_unbonding

* fix nomination pools

* fix node code

* add mock comments

* fix imports

* remove todo

* more fixes

* more fixes

* bench fixes

* more fixes

* more fixes

* import fix

* more fixes

* more bench fix

* refix

* refix

* Update primitives/staking/src/lib.rs

Co-authored-by: Kian Paimani <[email protected]>

* is_unbonding returns a result

* fix

* review fixes

* more review fixes

* more fixes

* more fixes

* Update frame/fast-unstake/src/benchmarking.rs

Co-authored-by: Squirrel <[email protected]>

* remove redundant CurrencyBalance from nom-pools

* remove CB

* rephrase

* Apply suggestions from code review

* Update frame/nomination-pools/src/tests.rs

* finish damn renamed

* clippy fix

* fix

Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: kianenigma <[email protected]>
Co-authored-by: parity-processbot <>
Co-authored-by: Squirrel <[email protected]>