[Staking] Currency <> Fungible migration

[Ank4n]

Migrate staking currency from traits::LockableCurrency to traits::fungible::holds.

Resolves part of #226.

Changes

Nomination Pool

TransferStake is now incompatible with fungible migration as old pools were not meant to have additional ED. Since they are anyways deprecated, removed its usage from all test runtimes.

Staking

• Config: Currency becomes of type Fungible while OldCurrency is the LockableCurrency used before.
• Lazy migration of accounts. Any ledger update will create a new hold with no extra reads/writes. A permissionless extrinsic migrate_currency() releases the old lock along with some housekeeping.
• Staking now requires ED to be left free. It also adds no consumer to staking accounts.
• If hold cannot be applied to all stake, the un-holdable part is force withdrawn from the ledger.

Delegated Staking

The pallet does not add provider for agents anymore.
TODO: check again if unclaimed withdrawals would be affected by this.

Migration stats (needs update)

Polkadot

Total accounts that can be migrated: 59564
Accounts failing to migrate: 1
Accounts with some stake force withdrawn: 59
Total force withdrawal: 29591.26 DOT

Kusama

Total accounts that can be migrated: 26311
Accounts failing to migrate: 0
Accounts with some stake force withdrawn: 48
Total force withdrawal: 1036.05 KSM

Full logs here.

Note about locks (freeze) vs holds

With locks or freezes, staking could use total balance of an account. But with holds, the account needs to be left with at least Existential Deposit in free balance. This would also affect nomination pools which till now has been able to stake all funds contributed to it. An alternate version of this PR is #5658 where staking pallet does not add any provider, but means pools and delegated-staking pallet has to provide for these accounts and makes the end to end logic (of provider and consumer ref) lot less intuitive and prone to bug.

This PR now introduces requirement for stakers to maintain ED in their free balance. This helps with removing the bug prone incrementing and decrementing of consumers and providers.

TODO

• Test: Vesting funds can be staked.
• Permissionless call to release lock.
• Migration of consumer (dec) and provider (inc) for direct stakers.
• force unstake if hold cannot be applied to all stake.
• Fix try state checks (it thinks nothing is staked for unmigrated ledgers).
• Bench migrate_currency.
• Virtual Staker migration test.
• Ensure total issuance is upto date when minting rewards.

Followup

• Ensure nomination pool members can directly stake and vice versa. #5742

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/12069377708
Failed job name: test-linux-stable

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/12069377705
Failed job name: cargo-clippy