* Draft for new design of NPoS rewards

* finish code

* fix test

* add tests

* improve log test

* version bump

* Update srml/staking/reward-curve/Cargo.toml

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* u128 -> u64

* make conversion to smaller type safe

* Update core/sr-primitives/src/curve.rs

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>