JIT-funded TWAP from EOA via ComposableCowPoller

[anxolin]

Follow-up to #12 (TWAP from EOA), adding just-in-time funding of funds.

In #12 the full TWAP sell amount had to flow into cow-shed up front, which is capital-inefficient for TWAPs/DCA that span long periods. Here the capital stays in the user's EOA and each part is pulled just before it settles via the ComposableCowPoller contract (see cowprotocol/composable-cow#116).

How it works

1. A minimal sell=buy order (BUY 1 wei of sDAI with sDAI) carries a gasless post-hook that, via cow-shed: approves the Vault Relayer and creates the TWAP (createWithContext, so t0 is anchored to the settlement block). The TWAP is owned by cow-shed; proceeds go back to the EOA. Now that sell==buy is supported, no extra intermediate token is needed.
2. The EOA approves the ComposableCowPoller for the full TWAP sell amount and registers the funding schedule (register(ctx, {handler, funder: EOA, owner: cow-shed, staticInput})).
3. Before each part settles, the watch-tower calls poller.topUp(ctx), which pulls exactly that part's sell amount from the EOA into cow-shed.

This removes both drawbacks noted in #12: it is capital-efficient, and it no longer depends on a distinct sell/buy token for the setup order.

Notes

• topUp is left to the watch-tower (it cannot live in the TWAP's own appData: the hook embeds ctx, but ctx derives from the appData hash — a cycle).
• Requires the cow-sdk patch from the base branch (End-end script to post TWAP from EOA #12) to be present for yarn install to patch the SDK.

Test

Requirements: set PRIVATE_KEY and RPC_URL_100 in .env; the EOA needs ≥ ~0.21 sDAI on Gnosis (0.2 TWAP + dust for the sell=buy order fee).

yarn dev   # runs postTwapForEOAWithJitFunds

Then watch the cow-shed orders in the explorer (printed by the script) as each part is funded and settled.