Bound staking storage items (#12230)

* replace pallet level unboundedness to individual storage items

* bound structs

* bounding history depth

* defensive error

* use the era history depth from config

* clean up history depth from storage in v11

* keep the name HistoryDepth for the new configuration value

* use u32 for history depth in node runtime

* improve doc comments

* add HistoryDepth to mock runtimes with pallet-staking

* rustfmt

* refactor and doc improve

* apply re-benchmarked weight for staking

* pr feedback improvements

* test for claimed rewards following the expected bounds

* refactor test to calculate first and last reward era programmatically

* verify previous eras cannot be claimed

* add migration v12

* ".git/.scripts/bench-bot.sh" pallet dev pallet_staking

* fix compiler error

* corrupting history depth does not lead to catastrophic issue

* fix new line

* remove unused import

* fmt

* add test to document scenario where history depth is reduced without migration

* fmt

* Update frame/staking/src/lib.rs

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

* Update frame/staking/src/migrations.rs

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

* doc for all storage items bounded by HistoryDepth

* Update frame/staking/src/pallet/mod.rs

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

* Update frame/staking/src/tests.rs

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

* pr feedback fixes

* Update frame/staking/src/tests.rs

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

* remove extra checks

* fix merge

* fmt

Co-authored-by: command-bot <>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: kianenigma <kian@parity.io>

substrate/frame/staking/src/slashing.rs

@@ -53,7 +53,7 @@ use crate::{
 	BalanceOf, Config, Error, Exposure, NegativeImbalanceOf, Pallet, Perbill, SessionInterface,
 	Store, UnappliedSlash,
 };
-use codec::{Decode, Encode};
+use codec::{Decode, Encode, MaxEncodedLen};
 use frame_support::{
 	ensure,
 	traits::{Currency, Defensive, Get, Imbalance, OnUnbalanced},
@@ -182,7 +182,7 @@ impl SlashingSpans {
 }
 
 /// A slashing-span record for a particular stash.
-#[derive(Encode, Decode, Default, TypeInfo)]
+#[derive(Encode, Decode, Default, TypeInfo, MaxEncodedLen)]
 pub(crate) struct SpanRecord<Balance> {
 	slashed: Balance,
 	paid_out: Balance,