[Enhancement] Convert fast-unstake to use StakingInterface, decouplin…

[ruseinov]

Resolves https://github.com/paritytech/substrate/issues/12337 or rather what's left of it. As we decided not to support pool joins at the moment we can probably ignore that requirement?

[ruseinov]

bot rebase

[paritytech-processbot[bot]]

Rebased

[ruseinov]

@kianenigma this needs your attention now. I've done fixes to nomination-pools and fast-unstake, only the tests/benches are failing now, but I'd like to verify the approach first.

[ruseinov]

bot rebase

[paritytech-processbot[bot]]

Rebased

[ruseinov]

@kianenigma I have addressed all the comments except for halt and the controller stuff.

I think this is outside of the scope of this PR (halt - because it's already implemented in another one, controller - because it's already released in the original version of fast-unstake, so it has little to do with the work we are doing here).

Let me know if this makes sense.

[ruseinov]

bot rebase

[paritytech-processbot[bot]]

Rebased

[kianenigma]

renamed a few trivial things, LGTM otherwise.

[ruseinov]

bot merge

[paritytech-processbot[bot]]

Error: "Check reviews" status is not passing for https://github.com/paritytech/polkadot/pull/6199

[ruseinov]

bot merge