Speed up nominator state checks in staking pallet (#2153)
Should help https://github.com/paritytech/polkadot-sdk/issues/234. Related to https://github.com/paritytech/polkadot-sdk/issues/2020 and https://github.com/paritytech/polkadot-sdk/issues/2108. Refactors and improves running time for try runtime checks for staking pallet. Tested on westend on my M2 pro: running time drops from 90 seconds to 7 seconds.