AToken DCA optimization for budgeted schedule

[dmoka]

Transfers from borrowing account are expensive and holding account is not borrowing anything

FOr budgeted DCA we could do a optimization by transfering reserved balance straight to the DCA and bypassing account that would require that extra gas

Original issue: #1195

[dmoka]

Some in progress specs

2. Pallet Account Execution Model (Budgeted DCAs)

Purpose

Reduce gas costs by avoiding repeated ERC20 transfers through the user account, which may be a gas-heavy smart contract.

Implementation

• For budgeted DCAs, the full input budget is transferred once to the DCA pallet account: T::Currencies::transfer(user → dca_pallet)

• Per-schedule balances are tracked in: DcaBalances<ScheduleId, Balance>

• All per-period operations use the pallet account as the origin:

• Fee deductions

• ERC20 transfers to AMMs

• Swap execution

• No reserve/unreserve logic is used for budgeted schedules.

• On schedule completion/termination:

• Any remaining pallet balance is returned to the user.

For unbudgeted DCA:

• The system keeps using reserve/unreserve + user account transfers.
• Extra gas mechanism still applies to prevent failures.