Add asset identifier for `totalReceiveAmount` in `AssetTransferInstructions`

[lucasrosa90]

Problem

AssetTransferInstructions includes totalReceiveAmount (the amount the recipient will receive after fees), but there is no field indicating which asset that amount is denominated in.

For same-asset transfers (e.g., USDC -> USDC), this is implicitly understood. However, for cross-asset transfers (e.g., USDC -> USDT, BRL -> USDC), the consumer has no way to know which asset totalReceiveAmount refers to.

Existing pattern

AssetFeeBreakdown already solves this problem for fees:

{
  "assetFee": {
    "lineItems": [{ "value": "2000", "purpose": "VALUE_VARIABLE", "asset": "$USDC" }],
    "totalPricedIn": "$USDC",
    "total": "2000"
  }
}

total is the amount, and totalPricedIn identifies the asset.

Proposal

Add a companion field to totalReceiveAmount that identifies the asset, following the same pattern as fees. For example:

// In AssetTransferInstructions (common.ts L586-602)
{
  assetFee: string | AssetFeeBreakdown;
  totalReceiveAmount?: string;
  totalReceiveAmountAsset?: MovableAssetSearchCanonical; // <-- new field
}

Naming options

Option	Pros	Cons
totalReceiveAmountAsset	Explicit, directly pairs with totalReceiveAmount	Verbose
receiveIn	Concise, mirrors totalPricedIn concept	Less explicit about what it pairs with
totalReceiveAmountPricedIn	Consistent with totalPricedIn naming	Very verbose

[ezraripps]

I am not sure if this is correct because I would imagine it would always be in the to asset

[rkeene]

If we did do this, it should follow the rest of our standard for amounts. An amount should be an object with the properties of the amount (token, magnitude/value, etc).