staking: Flexible generation of reward curve and associated tweaks (#8327)

* Initial abstraction

* Alter rest of APIs

* Fixes

* Some extra getters in Gilt pallet.

* Refactor Gilt to avoid u128 conversions

* Simplify and improve pow in per_things

* Add scalar division to per_things

* Renaming from_fraction -> from_float, drop _approximation

* Fixes

* Fixes

* Fixes

* Fixes

* Make stuff build

* Fixes

* Fixes

* Fixes

* Fixes

* Update .gitignore

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

* Update frame/gilt/src/lib.rs

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

* Update frame/gilt/src/mock.rs

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

* Fixes

* Fixes

* Fixes

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

substrate/frame/session/benchmarking/src/mock.rs

@@ -175,7 +175,7 @@ impl pallet_staking::Config for Test {
 	type SlashCancelOrigin = frame_system::EnsureRoot<Self::AccountId>;
 	type BondingDuration = ();
 	type SessionInterface = Self;
-	type RewardCurve = RewardCurve;
+	type EraPayout = pallet_staking::ConvertCurve<RewardCurve>;
 	type NextNewSession = Session;
 	type ElectionLookahead = ();
 	type Call = Call;

substrate/frame/session/src/lib.rs

@@ -177,12 +177,12 @@ impl<
 		// (0% is never returned).
 		let progress = if now >= offset {
 			let current = (now - offset) % period.clone() + One::one();
-			Some(Percent::from_rational_approximation(
+			Some(Percent::from_rational(
 				current.clone(),
 				period.clone(),
 			))
 		} else {
-			Some(Percent::from_rational_approximation(
+			Some(Percent::from_rational(
 				now + One::one(),
 				offset,
 			))