[WIP] Move era reward minting to DAP with era-based allocation in Staking

[Ank4n]

Partially implements: https://hackmd.io/@jonasW3F/rkN6BXE2ex

Overview

This PR moves era reward minting logic from pallet-staking-async to pallet-dap as well as introducing budget allocation management to DAP. Closing #10833 in favour of this since the era pot management belongs to staking.

Changes

Functional

• Transfers minting responsibility to pallet-dap exclusively
• DAP pre-allocates rewards at era start into dedicated pot accounts per era
• Staking transfers from era pots via StakingRewardProvider trait instead of minting on-the-fly
• DAP: Introduces configurable budget allocation: splits total inflation between staker rewards, validator incentives, and buffer.
• Implements hard deprecation of staking legacy minting code path.
• Round down era reward to ensure it never exceeds the budget (this was a minor bug in existing code)

Traits

• StakingRewardProvider: Enables staking to request era reward allocation (minting + funding pots).
• UnclaimedRewardSink: Specifies destination for unclaimed rewards when era pots are cleaned up after history depth expires.
• EraPayoutV2: Succeeds EraPayout returning single era emission value (instead of tuple of (staking, treasury) split) that DAP can budget internally.

Non-Changes

• Era inflation calculation logic remains in the runtimes (only the staker/treasury split logic changes)

Runtime Integration

Runtimes need to make the following changes:

1. Add EraPayoutV2 implementation to pallet-dap::Config
2. Replace staking_async::Config::EraPayout with RewardProvider = Dap
3. Update runtime inflation logic to return total era emission (without splitting)

Out of Scope

• Treasury Budget Management
• Stables payout to validators (and collators)

---

TODO

• DAP manages budgets
• Move minting to DAP
• Hard deprecate legacy minting in Staking pallet.
• Era based pot accounts in Staking
• Separate Staker and Validator budget
• Track validator total self stake
• Self stake incentive calculation logic
• Vested Transfer of Validator Incentive Reward
• Get rid of commission

[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/21154685172
Failed job name: test-linux-stable