feat(cketh): drive the sweeper transaction pipeline from its own timer task

[gregorydemay]

DEFI-2926, stacked on #11144 which instantiates the pipeline this drives.

Why

#11144 gives the sweeper address its own transaction pipeline, but nothing moves requests through it. This is the task that does.

What

sweep::process_sweeper_transactions runs the sweeper pipeline through the same create → sign → send → resubmit → finalize cycle as withdrawals, signing with the sweeper derivation path [3] and reading the sweeper address' own transaction count. It takes its own TaskType::SweeperSend timer guard, so a slow sweep round cannot block the withdrawal task or be blocked by it — which is the point of the separate nonce sequence in the first place.

The first commit is a prerequisite worth reading on its own: four RPC helpers in withdraw were implicitly about the main address, calling minter_address() themselves or keying receipts by LedgerBurnIndex. Reading a transaction count, broadcasting signed transactions and fetching finalized receipts are none of them specific to a sender or to what a request is keyed by, so they take the sender as an argument and the receipt fetch becomes generic over the pipeline id. Behaviour is unchanged: the receipt loop moves into fetch_finalized_receipts, which returns None where the loop used to return early.

SweepRequest::Error being Infallible pays off here: creating a sweep transaction is destructured with let Ok(transaction) = ..., with no arm for a failure the type system rules out. That is what #11178 made possible by turning the creation error into an associated type.

Scope

Nothing enqueues a SweepRequest yet, so the task early-returns on an empty pipeline and this is inert in production. Still to come: the sweep-queue→SweepRequest source, EIP-7702 (0x04) first-time delegation, and gating on prepaid sweep gas. EIP-1559 (0x02) only.

Note for reviewers

The sweep driver and the withdrawal driver are now near-identical five-stage loops over different request types, down to a private trio of batch-size constants that are 5 in both files. Deduplicating them is the obvious follow-up now that the pipeline is generic, but it would bury this change, so it is deliberately left for its own PR.

[Copilot]

Pull request overview

Adds an independent timer-driven transaction pipeline for the ckETH sweeper address.

Changes:

• Adds the sweeper create/sign/send/resubmit/finalize driver.
• Generalizes withdrawal RPC helpers by sender and pipeline ID.
• Registers a dedicated timer guard and periodic task.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
withdraw.rs	Generalizes shared RPC helpers.
sweep.rs	Implements the sweeper pipeline driver.
state/transactions/tests.rs	Reuses the sweeper gas-limit constant.
state.rs	Adds sweeper address access and task type.
main.rs	Registers the sweeper timer.
lib.rs	Exports the sweep module.
deposit_address/mod.rs	Exposes the sweeper derivation path internally.

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