dApp Staking v3 - Rewards As Tree

[Dinonard]

Pull Request Summary

Replaces the sorted vector for rewards, with a BTreeMap.
This allows for efficient removal of entries from the tree, once reward has been claimed.

Error DAppRewardAlreadyClaimed has been removed.
Once dApp reward has been claimed for an era, further claim calls will result in
NoClaimableRewards error.

Also includes a minor storage migration, only to be used on Shibuya.
Moved all migration logic under a new module, for better readability.

Benchmarks will be re-run at another time.

[ashutoshvarma]

Looks good!
Minor nitpick comment

[github-actions]

Package	Line Rate	Branch Rate	Health
precompiles/xvm/src	74%	0%	➖
precompiles/sr25519/src	64%	0%	➖
precompiles/dapp-staking-v3/src	90%	0%	✔
primitives/src	66%	0%	➖
pallets/dynamic-evm-base-fee/src	81%	0%	✔
primitives/src/xcm	66%	0%	➖
precompiles/substrate-ecdsa/src	74%	0%	➖
chain-extensions/xvm/src	0%	0%	❌
chain-extensions/types/assets/src	0%	0%	❌
precompiles/assets-erc20/src	81%	0%	✔
pallets/dapps-staking/src/pallet	85%	0%	✔
precompiles/unified-accounts/src	100%	0%	✔
chain-extensions/unified-accounts/src	0%	0%	❌
pallets/dapp-staking-migration/src	39%	0%	❌
chain-extensions/pallet-assets/src	0%	0%	❌
pallets/dapp-staking-v3/src/test	0%	0%	❌
chain-extensions/types/unified-accounts/src	0%	0%	❌
pallets/collator-selection/src	69%	0%	➖
pallets/xc-asset-config/src	53%	0%	➖
precompiles/dapps-staking/src	94%	0%	✔
pallets/unified-accounts/src	84%	0%	✔
pallets/xvm/src	40%	0%	❌
pallets/dapp-staking-v3/rpc/runtime-api/src	0%	0%	❌
pallets/inflation/src	70%	0%	➖
pallets/dapp-staking-v3/src/benchmarking	0%	0%	❌
pallets/dapp-staking-v3/src	76%	0%	➖
pallets/ethereum-checked/src	48%	0%	❌
chain-extensions/types/xvm/src	0%	0%	❌
pallets/dapps-staking/src	81%	0%	✔
pallets/block-rewards-hybrid/src	87%	0%	✔
precompiles/xcm/src	72%	0%	➖
precompiles/dapp-staking-v3/src/test	0%	0%	❌
Summary	67% (3171 / 4715)	0% (0 / 0)	➖

Minimum allowed line rate is 50%