fix: include tips in the fulfiller's balance and approval checks

[Dusk1e]

Problem

fulfillOrder and fulfillOrders build the fulfiller's balance and approval set from the order's own items only:

items: [...offer, ...consideration]

The checks that read that set sum tips in alongside the consideration. So a tip in a token the order does not already carry has no entry to look up, and findBalanceAndApproval throws before any transaction is built:

Checking for balance and approvals for token 0x0000000000000000000000000000000000000000 id 0 failed

That rules out a native tip on an ERC20 listing, a tip in a second ERC20, and NFT tips, all of which Seaport itself accepts. Tipping in the same token as the order works fine, which is why the existing tip coverage in partial-fulfill.spec.ts never hit this.

Fix

Include the mapped tip items in the fulfiller's lookup set in both entry points. They go on the end, after the order's items, so the offer and consideration criteria mapping in getItemToCriteriaMap is untouched.

It also makes the check do its job rather than just stop crashing: a tip in a token the fulfiller has not approved now produces its own approval action, which the fulfillment would revert without.

In fulfillOrders the per-order tip mapping is hoisted so it is built once and reused for both the lookup set and ordersMetadata, instead of mapped twice.

Test

test/tips.spec.ts covers both entry points. Both fail on main with the error above.

• fulfillOrder with a second-ERC20 tip: asserts both approval actions appear, then fulfills and checks the NFT and the tip both land.
• fulfillOrders with a native tip on an ERC20 listing: asserts the tip rides as msg.value, then fulfills and checks the recipient's balance moved.

Suite green at 174.