Chore: replace dead `apas` field with `foreignAssets` on extra-txn descriptors

[temptemp3]

Context

The extra-txn descriptors passed to ci.setExtraTxns() use apas: [assetId] to declare foreign assets. However, apas is not a field recognized by algosdk.makeApplicationCallTxnFromObject — the SDK expects foreignAssets. The apas field is silently ignored during transaction construction.

This hasn't caused issues in practice because:

• The swap flow (lib/builders.js) works via group resource sharing across the larger transaction group.
• The NNT200 withdraw (lib/nnt200.js) was switched to the "default" GRS strategy in Fix withdraw_nnt200 missing foreignAssets for underlying ASA #1, which carries assets via separate GRS helper transactions.

But the dead field is misleading to future readers who may assume it's doing something.

Locations

• lib/builders.js lines 213-214 (apas: [toAssetId])
• lib/builders.js line 219 (fields.apas = [toAssetId])
• lib/nnt200.js line 98 (apas: [assetId])

Suggested action

Investigate whether replacing apas with foreignAssets on the extra-txn descriptors is picked up by arccjs or algosdk. If it is, replace all occurrences. If not (because the "merge" strategy overrides foreignAssets anyway), document apas as intentionally inert and add a code comment explaining why it exists.

Related: #1