Const
Ref: https://github.com/paritytech/polkadot-sdk/blob/00b85c51dfbc0fecbb8a4dd3635d4c177a6527a6/substrate/frame/staking/runtime-api/src/lib.rs#L25-L33
Ref: https://github.com/paritytech/polkadot-sdk/blob/00b85c51dfbc0fecbb8a4dd3635d4c177a6527a6/substrate/frame/staking/runtime-api/src/lib.rs#L25-L33